JPH0474833B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the improvement of solid electrolyte batteries that use lithium as a negative electrode active material, such as lithium-lead iodide batteries, and aims to improve discharge characteristics. .

Conventional solid electrolyte batteries use a lithium plate as the negative electrode, but as discharge progresses, a gap forms between the negative electrode and the solid electrolyte layer, reducing the discharge utilization rate of the negative electrode and preventing sufficient discharge. The disadvantage is that performance cannot be obtained. This is because the discharge reaction of this type of battery is such that lithium gradually ionizes from the side facing the positive electrode on the negative electrode side, passes through the solid electrolyte layer, moves to the positive electrode side, reacts with the positive electrode active material, and produces discharge products on the positive electrode side. However, since the positive electrode does not expand in volume by an amount equivalent to the discharge consumption of the negative electrode, and the solid electrolyte has no elasticity, the solid electrolyte layer expands as the negative electrode is consumed due to discharge. This is because it cannot follow and deform.

Therefore, it is necessary to pressurize the negative electrode to maintain contact between the negative electrode and the solid electrolyte at all times, but in small and thin batteries, it is difficult to provide such a pressurizing means inside the battery.

In view of such circumstances, the present inventors have conducted various studies and found that Li ₃ N-LiI (Li ₃
A solid solution with a molar ratio of N and LiI of 0.88:0.12) was used, and the theoretical volume ratio of lithium powder and the above Li ₃ N-LiI powder (the theoretical volume of lithium obtained by dividing the weight of lithium by the density of lithium, ₃ The weight of N−LiI is Li ₃
When the negative electrode is constructed from a mixture with a specific ratio of Li ₃ (the ratio to the theoretical volume of N-LiI obtained by dividing it by the density of N-LiI), the discharge utilization rate of lithium is improved and the discharge characteristics are good. The inventors have discovered that a solid electrolyte battery can be obtained, and have completed the present invention.

That is, in the present invention, even if lithium near the solid electrolyte layer disappears as discharge progresses, the Li ₃ N-LiI as a solid electrolyte dispersed in the negative electrode allows lithium ions to migrate to the positive electrode side. By improving the discharge utilization rate of lithium, it was possible to obtain a solid electrolyte battery with good discharge characteristics.
More specifically, in the present invention, the current per unit area decreases by increasing the substantial contact area between lithium and the solid electrolyte, and as a result,
Because the diffusion rate of lithium approaches the consumption rate of lithium consumed at the interface (the interface between lithium and the solid electrolyte), lithium is less likely to peel off.
It is thought that the negative electrode utilization rate is improved.

The lithium powder is preferably a fine powder of 60 meshes or more, and the Li ₃ N-LiI used for the negative electrode is also preferably a fine powder of 60 meshes or more.

The negative electrode is made of these lithium powders and Li ₃ N-
After mixing with LiI powder at a predetermined ratio, approximately 0.1~
Pressure molded into the specified shape at a pressure of 1 t/cm ² . Note that, after the negative electrode and the solid electrolyte layer are each preformed, the negative electrode and the solid electrolyte layer can also be integrally formed by overlapping them and performing main molding.

In the present invention, Li ₃ N-LiI is used as a solid electrolyte to be mixed into the negative electrode _.
is composed of a solid solution of Li ₃ N and LiI in a molar ratio of 0.88:0.12. In the present invention, Li ₃ N-LiI is used as the solid electrolyte mixed into the negative electrode because Li ₃ N-LiI has higher conductivity than other solid electrolytes and has a low interfacial resistance at the interface with lithium. This is because, since it is small, it is easy to extract a large current and it is easy to obtain a battery with good discharge characteristics. Also,
Li ₃ N-LiI is also used as the solid electrolyte constituting the solid electrolyte layer for the same reason as above.

The mixing ratio of lithium powder and Li ₃ N-LiI powder in the mixture is Li ₃ N-LiI in theoretical volume ratio.
When the ratio of powder is x to 1 part of lithium powder, it is appropriate that x be in the range of 1<x<1.4. This is because if the ratio of Li ₃ N-LiI powder in the mixture of lithium powder and Li ₃ N-LiI powder is less than the above range, the effect of increasing the discharge utilization rate of the negative electrode and improving the discharge characteristics will not be fully exhibited. This is because if the ratio of Li ₃ N-LiI powder in the mixture exceeds the above range, the absolute amount of lithium in the negative electrode will decrease, resulting in a decrease in discharge capacity. Furthermore, considering the decrease in discharge capacity as x increases, it is particularly preferable that x satisfies 1<x<1.2.

Next, the present invention will be explained with reference to Examples.

Example 1 10g of lithium powder (140 mesh pass) and Li ₃ N
- Thoroughly mix 38.26 g of LiI powder (60 mesh passes) to form the lithium powder and Li ₃ N-LiI used for the negative electrode.
A mixture with powder in a theoretical volume ratio of 1:1.2 was obtained.

Note that the above Li ₃ N-LiI is a solid solution of Li ₃ N and LiI in a molar ratio of 0.88:0.12, and the density of this Li ₃ N-LiI is 1.703. Therefore, the theoretical volume of Li ₃ N-LiI is 22.47 cm ³ . The density of lithium is
0.534, and the theoretical volume of lithium is 18.73 ^cm3 . Therefore, the theoretical volume ratio of lithium powder to Li ₃ N-LiI powder is 1:1.2.

100 mg of Li ₃ N-LiI is used as a solid electrolyte layer, 450 mg of a mixture of lead iodide and carbonyl nickel (mixing ratio is 4:1 in theoretical volume ratio) is used as a positive electrode, and the theoretical volume of the lithium powder and Li ₃ N-LiI powder is Ratio 1:1.2
The mixture was weighed out so that the amount of lithium was 5.18 mg, and it was used as a negative electrode to form a power generation element using a pressure bonding method, and a solid electrolyte battery with a diameter of 16 mm and a thickness of about 1 mm as shown in Figure 1 was assembled. . In FIG. 1, 1 represents lithium powder and Li ₃ N-LiI as described above.
2 is a positive electrode, 3 is a solid electrolyte layer, 4 is a negative electrode current collector plate, 5 is a positive electrode current collector plate, 6 is a ceramic ring, and 7 is a brazing material.

When this battery was discharged at 20° C. and a constant current of 30 μA, the characteristics shown by curve A in FIG. 2 were obtained.

Comparative Example 1 A battery was assembled in the same manner as in Example 1 except that 5.18 mg of lithium powder (140 mesh passes) was weighed out and used as a negative electrode.

When this battery was discharged at a constant current of 30 .mu.A at 20.degree. C., the characteristics shown by curve B in FIG. 2 were obtained.

As is clear from the comparison between curve A and curve B shown in FIG. 2, by mixing Li ₃ N-LiI into the negative electrode, a battery with good discharge characteristics can be obtained.

Next, in order to clarify the effect of the mixing ratio of lithium powder and Li ₃ N-LiI powder on the discharge characteristics, lithium powder (14 mesh passes) and the same Li ₃ N-LiI powder (60 mesh passes) were mixed. Theoretical volume ratio is 1:0, 1:0.2, 1:0.4, 1:0.5, 1:
0.6, 1: 0.7, 1: 1.0, 1: 1.2, 1: 1.4, 1:
The mixture was weighed out so that the ratio was 1.8:1:2.0 and thoroughly mixed to obtain a mixture of lithium powder and Li ₃ N-LiI powder.

Example 1 Using 100 mg of Li ₃ N-LiI as a solid electrolyte
450 mg of a mixed powder of lead iodide and carbonyl nickel similar to the above was used as the positive electrode, and the lithium powder and Li ₃ N
−The mixture with LiI powder is
An amount of 5.18 mg (equivalent to 20 mAh) was weighed out and used as a negative electrode to form a power generating element by a pressure bonding method, and a battery similar to that in Example 1 was assembled.

This battery was discharged at 20°C with a constant current of 30μA.

An important characteristic of the negative electrode is the volume of the negative electrode required to discharge a certain electric capacity, and the smaller this value is, the better. In order to compare each battery with this characteristic, the above discharge results are shown in Figure 3. The theoretical volume mixing ratio (1:x) of lithium powder and Li ₃ N--LiI powder is plotted on the horizontal axis.

As is clear from FIG. 3, by adding Li ₃ N-LiI, the volume of the negative electrode required to ensure a certain discharge capacity becomes smaller than in the case of lithium alone (ie, when the ratio is 1:0). This effect is particularly noticeable when the Li ₃ N-LiI powder ratio x is 1<x
<1.4.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the solid electrolyte battery of the present invention, and FIG. 2 is a discharge characteristic diagram of the solid electrolyte battery of the present invention and a conventional solid electrolyte battery. FIG. 3 is a diagram showing the relationship between the theoretical volume mixing ratio of lithium powder and Li ₃ N-LiI powder and the volume per unit electric capacity of lithium/negative electrode utilization rate. 1... Negative electrode, 2... Positive electrode, 3... Solid electrolyte layer.

Claims (1)

[Claims] 1. A negative electrode 1 containing lithium as an active material, a positive electrode 2 disposed opposite to the negative electrode 1, and a solid electrolyte layer 3 interposed between the negative electrode 1 and the positive electrode 2. In the solid electrolyte battery, the solid electrolyte is Li ₃ N-LiI, and this Li ₃ N-
LiI is composed of a solid solution of Li ₃ N and LiI in a molar ratio of 0.88:0.12, and the negative electrode 1 is composed of a mixture of lithium powder and Li ₃ N-LiI powder, and the ratio of Li ₃ N to lithium powder in the mixture is - A solid electrolyte battery characterized in that, where x is the theoretical volume ratio of LiI powder to 1 lithium powder, x is in the range of 1<x<1.4. 2. The solid electrolyte battery according to claim 1, wherein x satisfies 1<x<1.2.