JPH0261963A - Lithium type heat battery - Google Patents

Abstract

PURPOSE:To enhance the discharge characteristic of a lithium type heat battery using an electrolytic liquid layer, wherein the electrolyte of a mixture of kalium chloride and lithium chloride is mixed with magnesium oxide, by selecting the electrolyte content of the mentioned electrolytic liquid layer so as to lie within a specified range. CONSTITUTION:A positive electrode plate is formed from iron disulfide while an electrolyte is formed by mixing magnesium oxide with a mixture of kalium chloride and lithium chloride, and a negative electrode consists of lithium- aluminum alloy. Such cells thus constituted are laminated and accommodated in a case to accomplish a lithium type heat battery. Therein the electrolyte content of the electrolytic liquid layer shall range between 60 and 80wt.% which will improve the discharge characteristic remarkably and enhance the energy density of heat battery.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a lithium-based thermal battery.

Conventional technology Lithium-based thermal batteries use metallic lithium or lithium alloy as the negative electrode active material, a mixture of potassium chloride and lithium chloride as the electrolyte, and a molten salt using iron disulfide or iron sulfide as the positive electrode active material. It is a type of high-temperature secondary battery. The electrolytic solution is mixed with HgO powder to form an electrolytic solution layer, and is fixedly held between the electrodes. In conventional thermal batteries, the content of the electrolytic solution contained in the electrolytic solution layer was about 60 wt% for reasons described later.

Problems to be Solved by the Invention In lithium-based thermal batteries, the electrolyte is mixed with HGO powder and fixedly held between the electrodes, so the amount of active material used in lithium thermal batteries is lower than that of other batteries in which one electrode is immersed in the electrolyte. The amount of electrolyte is extremely small. Generally, when the amount of electrolyte is reduced, the discharge voltage and active material utilization rate of the battery decrease, and the battery characteristics deteriorate. The larger the amount of this lick electrolyte, the better.

However, in the case of thermal batteries, dozens of single cells are stacked together to form a complete battery, so if the electrolyte layer becomes too soft due to too much electrolyte, the positive and negative electrode plates of the single cell may There were problems such as the electrolyte overflowing from between the electrodes and becoming the common electrolyte for the laminated cells.

Therefore, in the past, the amount of electrolyte was reduced as much as possible without adversely affecting the battery characteristics, and a composition of 60 wt χ of electrolyte and 4 (1 wt %) of HgQ in the electrolyte layer was used. Since there were no practical problems with the electrolyte, no detailed studies were conducted on increasing or decreasing the amount of electrolyte.

The inventor conducted research on increasing the battery energy density by further increasing the discharge current density of thermal batteries, and as a result found that with the conventional electrolyte layer composition, the battery characteristics deteriorate significantly at ultra-high rate discharge. In other words, the conventional composition does not cause a problem at a discharge current density of about 0.3 A/-, which is the typical discharge current density of a conventional thermal battery, but when ultra-high rate discharge of I A/aa or more is carried out, the electrolyte becomes insufficient. It was found that the battery voltage and active material utilization rate suddenly decreased.

Means for Solving the Problems The present invention is a lithium-based thermal battery using an electrolyte layer made of an electrolyte made of a mixture of potassium chloride and lithium chloride mixed with magnesium oxide. It is characterized in that the content of the electrolyte is more than 60 wt% and less than 80 wt%.

The following single cell test was conducted to investigate how to increase the electrolyte content of the working electrolyte layer and improve battery characteristics. A single cell test is a single cell consisting of one positive electrode plate and one negative electrode plate, sandwiched between copper blocks heated to a predetermined temperature, and discharged in an argon atmosphere to determine the effect of the amount of electrolyte on battery characteristics and the electrolyte. This test examines the strength of the layer.

The results are shown in FIG. As is clear from the figure, as the content of the electrolyte solution increased, the discharge voltage of the battery improved and the active material utilization rate also improved. However, the electrolyte content is 80w.
If it exceeds t%, the electrolyte layer becomes extremely weak.
A complete battery may cause the above-mentioned problems.

The reason why battery characteristics improve when the amount of electrolyte in the electrolyte layer is increased in ultra-high rate discharge is considered to be as follows.

In conventional thermal batteries, the internal resistance increases significantly as the battery discharges, and this is due to solid phase precipitation of discharge products and electrolyte components that exceed the melting limit inside the electrodes. It is believed that when the amount of electrolyte is increased at this time, the amount of dissolved material increases, thereby delaying the precipitation of the substance and reducing the increase in internal resistance of the electrode, thereby improving the discharge characteristics.

Example The invention will be explained below using preferred embodiments.

Iron disulfide was used as the positive electrode plate, a mixture of potassium chloride and lithium chloride was used as the electrolyte, and lithium aluminum alloy was used as the negative electrode plate. Twenty single cells were stacked together via a heat generating agent and housed in a battery case. In the lithium-based thermal battery, the electrolyte content of the electrolyte layer is set to 7wt%.
A closed thermal battery A of the present invention was manufactured. Next, it has basically the same configuration as thermal battery A, and the electrolyte content is 60 wt%.
And a thermal battery of 80WtX was manufactured. These will be referred to as thermal batteries B and C for comparison.

These thermal cells were discharged at -40°C with a discharge current density of IA/-. The results are shown in FIG. 2, which shows that thermal battery A of the present invention is thermal battery B for comparison.

It can be seen that it has superior characteristics such as higher discharge voltage and larger capacity than C. In thermal battery B, since the amount of electrolyte was too small, the internal resistance increased significantly due to the precipitation of discharge products, and the battery voltage and active material utilization rate decreased. In thermal battery C, the amount of electrolyte was too large and the electrolyte overflowed from the electrolyte layer and became a common electrolyte, causing a short-circuit current to flow within the battery and causing a sudden drop in battery voltage.

Effects of the Invention As described above, the present invention can significantly improve the ultra-high rate discharge performance of a lithium-based thermal battery, thereby making it possible to improve the energy density of the thermal battery.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the influence of the electrolyte content of the electrolyte layer on single cell characteristics, and FIG. 2 is a diagram showing the discharge characteristics of a thermal battery according to the present invention and a thermal battery for comparison. α/1 Voltage / v Tsubo Σ Time / Cane

Claims (1)

[Claims] 1. A lithium-based thermal battery using an electrolyte layer formed by mixing magnesium oxide with an electrolyte consisting of a mixture of potassium chloride and lithium chloride, wherein the content of the electrolyte in the electrolyte layer is 60 wt% or less. A lithium-based thermal battery characterized in that the content of the lithium-based thermal battery exceeds 80 wt%.