JPS62139268A - Thermal battery - Google Patents

Abstract

PURPOSE:To reduce heat capacity of negative electrode and quicken voltage rising time by using a lithium-boron alloy negative electrode in which lithium- boron alloy is arranged inside a metal cup and the alloy is surrounded with a metal powder molding having electron conductivity and metal cup. CONSTITUTION:A negative active material 1 consists of a lithium-boron alloy sheet and arranged inside a metal cup 3. A metal powder molding 2 consists of metal alone or a mixture of metal powder and the powder mainly comprising electrolyte, and covers the surrounding of the lithium-boron alloy sheet with the metal cup 3. The metal powder used is necessary to be not alloyed of difficult to be alloyed with lithium, and iron nickel, stainless steel, or nichrom, or a mixture of these material is effectively used. The negative electrode is combined with an electrolyte layer 4, a positive mix layer 5, and a positive current collector 6 to form a unit cell.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to the structure of a lithium boron alloy negative electrode body for thermal batteries.

A conventional thermal battery is a type of high-temperature battery that uses a molten salt, which is solid at room temperature, as an electrolyte and heats it to a high temperature of about 400-700''C to liquefy it to generate electricity.

Conventional thermal batteries have used metal calcium, metal magnesium, etc. as negative electrode active materials, but these negative electrode active materials can handle the high current density discharge required for thermal batteries in recent years, such as 500 mA/7 for several minutes. It was impossible to satisfy the requirement of discharge life. In recent years, new lithium negative electrodes have been developed to solve these problems. However, although metallic lithium is active, it has a low melting point (181°C) and a battery operating temperature range (usually 400°C to
At 700"C), the liquid is completely converted to a single volume, which has the disadvantage of easily leaking out of the unit cell and causing an internal short circuit. Therefore, in the past, US Pat. No. 4,221,849 Add metal powder to molten lithium and mix uniformly as shown in
A structure has been proposed in which lithium is held on the surface of the metal powder and the lithium is surrounded by a sheet-shaped lithium negative electrode, a metal cup, and a molded metal powder to prevent lithium from flowing out.

Problems to be Solved by the Invention However, these methods require a considerable amount of metal powder to prevent lithium from flowing out, and (1) the heat capacity of the negative electrode increases and the thickness of the negative electrode increases. Because the heat conduction from the battery is delayed, it takes time to heat up the unit cell, and the rise time to the specified voltage is delayed.

(2) The weight of the negative electrode itself increases, but the heating agent for heating the unit cell must also increase, which increases the burden on the battery.

This problem arose and became a major drawback.

The present invention solves these problems.

Means for Solving the Problems In order to solve the above-mentioned problems, in the present invention, a lithium boron alloy is disposed on the inner surface of a metal cup, and a metal powder molded body having electronic conductivity and a metal cup are combined. It uses a lithium boron alloy negative electrode with an enclosed structure.

It has been found that when the working lithium-boron alloy has a weight ratio of 42.8% or more, it consists of two phases: a porous Li, B6 skeleton and metallic lithium held therein. Therefore, it has been reported that a lithium boron alloy with a Li weight ratio of 42.8% or more exhibits the potential of pure lithium until the metallic lithium contained therein is exhausted.
The characteristics of a thermal battery using an alloy with a weight ratio of 66 to 70% have also been reported (30 T HPower 5ourc
es SymposiumLithium-Boron
A11oy Anodes for Thermal
y-Activated Batteries).

However, when a lithium-boron alloy having such a composition is rolled into a sheet, the Li and B6 skeletons are destroyed and free lithium therein comes to the surface, causing lithium to flow out. Furthermore, in a lithium boron alloy with a Li weight ratio of 7Q% or more, there are few Li and B6 skeletons and the lithium retention capacity is low, so leakage still occurs.

Therefore, according to the configuration of the present invention, the lithium that flows out from the lithium boron alloy when the battery is operated can be prevented from flowing out by the metal powder molded body and the metal cup that surround it. The metal powder molded body is manufactured to have minute voids, and the lithium that has melted and flowed out is sucked up by capillary action into these voids, and is held in the pores within the metal powder molded body by the surface tension of the lithium. becomes. Therefore, when the battery is active, the metal powder molded body becomes a current collector that absorbs and holds molten lithium, and the lithium trapped therein is gradually consumed by discharge. Therefore, this lithium negative electrode is an active one with good current collection efficiency, and is also a stable one that does not cause lithium outflow.

6 b/゛Although the device previously proposed by the present inventors prevents lithium from flowing out by a similar effect, in the present invention, since lithium boron itself has a certain degree of lithium retention ability,
This allows the amount of surrounding metal powder compacts to be reduced.

EXAMPLES Hereinafter, examples of the present invention will be explained with reference to the drawings. FIG. 1 is an embodiment of the present invention, and is a longitudinal sectional view of a negative electrode. As is clear from FIG. 1, reference numeral 1 denotes a negative electrode active material made of a lithium boron alloy sheet, which is arranged on the inner surface of a metal cup 3. A metal powder molded body 2 is composed of either only metal powder or a mixed powder of metal powder and powder mainly composed of an electrolyte, and it surrounds the entire periphery of the lithium boron alloy sheet 1 together with the metal cup 3. The metal powder used here either does not form an alloy with lithium or is difficult to form, so iron, nickel, stainless steel, nichrome alone or a mixture of several of them or an alloy thereof have been effective.

A metal powder that readily alloys with lithium, Example 7B.

If aluminum or the like is used, the battery will immediately become alloyed and shattered when activated, resulting in problems such as lithium not producing the high potential inherent to lithium, losing activity, and causing volume changes.

FIG. 2 shows a unit cell constructed by combining the negative electrode body shown in FIG. 1 with an electrolyte layer 4, a positive electrode mixture layer 6, and a positive electrode current collector plate 6. The electrolyte layer 4 is an electrolyte, for example, KCe-
It is made by molding a powder in which LICe eutectic salt is held in an inorganic adsorbent such as MgO, and the positive electrode mixture layer 5 is a mixture layer of a positive electrode active material, an electrolyte, and an inorganic adsorbent. In this example, FeS2 was used as the positive electrode active material, KC (1-LICe eutectic salt as in the electrolyte layer 4) was used as the electrolyte, and SiO2 powder was used as the inorganic adsorbent. It is also possible to combine the individual pressure molded products, or to mold the electrolyte powder on top of the separately made negative electrode, and then mold the positive electrode mixture layer on top of that to form a three-layer structure. An iron plate was used as the positive electrode current collector plate 6.In the metal powder molded body 2 made only of metal powder, molten lithium exuded from the lithium boron alloy is sucked up and cannot be used as a battery unless it reaches the interface of the electrolyte layer 4. It does not work. In this case, it takes a long time for the battery to generate the specified voltage. Therefore, in order to shorten this time, we tried a method in which the metal powder molded body 2 contains an electrolyte component. In this case, the electrolyte The powder itself is mixed and adsorbed with the metal powder, or a powder with an electrolyte held in an inorganic adsorbent is mixed with the metal powder.By doing so, the electrolyte is also present on the surface of the lithium boron alloy sheet 1. Therefore, even before the molten lithium is sucked up into the metal powder compact 2, the added electrolyte acts as an ion conductor and can operate as a battery, shortening the rise time to the aforementioned predetermined voltage.

However, if too large a quantity of electrolyte component is added, the metal powder molded body 2 will lose its shape, so it is preferable to keep the electrolyte component within 3% by weight.

Furthermore, if the number of metal powder compacts 2 is too large or too small compared to the lithium boron amalgam 1, the following problems will occur. That is, if the amount of the metal powder molded body 2 is too large compared to the lithium boron alloy 1, the outflow prevention ability will be improved, but the discharge life will be significantly shortened and it will become unusable.

On the other hand, if the amount is too low, the leakage prevention ability will be reduced and lithium will leak out of the unit cell, causing a problem. Therefore, in this example, the weight ratio of the metal powder compact 2 and the lithium 1 is 50:6.
It is limited to 0 to 90:10.

In the composition of the lithium boron alloy, if the Li weight ratio is less than 66%, there is little free lithium (approximately 0 to 26% of Li L of the lithium boron alloy weight is not included), and the discharge life is significantly shortened.

In addition, alloys with a Li content of over 90% are mostly lithium and do not have the ability to retain lithium, and require a large amount of metal powder compacts, as in the case of conventional structures using pure lithium. The purpose of this invention cannot be achieved. Therefore, the lithium weight ratio in the lithium boron alloy is 66-90
It is preferable to adjust it to %.

The lithium outflow situation and voltage rise characteristics of the unit cell configured as described above were evaluated.

Table 1 compares this example with a conventional negative electrode (with a weight ratio of lithium and metal powder compact of 85+15). In this example, a lithium boron alloy with a Li weight ratio of 70% was used. one with a weight ratio of metal powder molded body and lithium boron alloy of 60 + 40 (indicated by A), and 4.
The discharge current density soomA/ for the one with a ratio of 0:60 (indicated as B) and the one with an ratio of 95:6 (indicated as C)
This figure shows the voltage rise time, discharge life, and lithium outflow situation after a discharge of m. The discharge test was performed 10 times each.

Table 1 11 As is clear from the table, Examples B and 0, in which the weight ratio of the metal powder molded body and the lithium boron alloy was outside the range of the present invention, were 40:60, an example in which the lithium boron alloy was large. In case B, leakage occurs and it cannot be used, and in example C, which has a ratio of 96:5 and a small amount of lithium boron alloy, although there is no outflow, the capacity is too small compared to other examples at the same weight, and it is obvious that it is not practical.

Effects of the Invention As described above, the negative electrode according to the present invention has the following advantages: (1) Since the lithium boron alloy itself has a certain degree of lithium retention ability, it reduces the number of particles of the metal powder molded body that retains melted and leaked lithium compared to the conventional example. This makes it possible to reduce the heat capacity of the negative electrode and speed up the voltage rise time.

(2)) Since it is possible to reduce the amount of metal powder molding, not only the weight of the negative electrode is reduced, but also the amount of heating agent can be reduced, resulting in a reduction in the weight of the battery.

Effects such as this can be obtained.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a negative electrode in an embodiment of the present invention, and FIG.
The figure is a longitudinal cross-sectional view of a unit cell using the negative electrode. 1... Lithium boron alloy, 2... Metal powder molded body, 3... Metal cup, 4... Bent electrolyte layer, 6... Positive electrode mixture layer.

Claims (6)

[Claims] (1) A thermal battery having a negative electrode structure in which a lithium boron alloy, which is a negative electrode active material, is disposed on the inner surface of a metal cup and is surrounded by a metal powder molded body and a metal cup. (2) The thermal battery according to claim 1, wherein the metal powder is a metal that is difficult to alloy with lithium. (3) The thermal battery according to claim 1, wherein the metal powder molded body contains an electrolyte component. (4) The thermal battery according to claim 1, wherein the metal powder is at least one selected from the group of iron, nickel, stainless steel, and nichrome, or an alloy thereof. (5) Lithium weight ratio without lithium boron alloy is 66
Thermal cell according to claim 1, limited to ~90%. (6) The thermal battery according to claim 1, wherein the weight ratio of the metal powder molded body and the lithium boron alloy is limited to 50:50 to 90:10.