JPH0782860B2 - Thermal battery - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal battery in which a heating agent is incorporated inside a battery and the heating agent is ignited when the battery is used to heat the inside of the battery to a high temperature for activation. Thus, a thermal battery having a high capacity and capable of discharging for a long time and having a high energy density is provided.

2. Description of the Related Art A thermal battery is a battery containing a heat generating agent and using a molten salt as an electrolyte. Since the electrolyte is a non-conducting solid salt during storage, it is in an inactive state as a battery, but by burning a heating agent to heat the inside of the battery to a high temperature, the electrolyte melts and exhibits conductivity. And the battery is activated.

A thermal battery is a type of storage battery that has little self-discharge during storage, can be stored for a long period of time, and can be instantly activated when necessary. Also, −55 to 100 ° C
It is a high energy density battery that can be used under a wide range of environmental temperatures. Since the thermal battery in the inactive state has a high internal resistance, it can be incorporated in the device with the load connected to the terminal. Due to such many features, thermal batteries have become indispensable as power sources for missiles, rockets, and other flying objects, and various emergency power sources.

Conventionally, a system using calcium for the negative electrode and calcium chromate for the positive electrode has been used as the active material of this type of thermal battery, but for higher capacity and high output, lithium or lithium alloy is used for the negative electrode. Thermal batteries using sulfides have been developed.

As the lithium alloy, an alloy of lithium and boron, aluminum, silicon, iron, gallium, germanium or the like can be used.

Iron sulfide, which has high heat resistance, is mainly used as the sulfide of the positive electrode active material, but nickel, chromium, cobalt,
Sulfides of copper, tungsten, molybdenum, etc., and sulfides of the Svrel phase containing these metals can also be used.

As the electrolyte, a eutectic salt of LiCl-59 mol% and KCl-41 mol% is generally used. This eutectic salt is relatively inexpensive, has a low melting point of 352 ° C., and has high insulation resistance at room temperature. As the electrolyte, a material obtained by mixing lithium in the negative electrode with an insulating powder such as magnesium oxide, boron oxide, or zirconium oxide having corrosion resistance so as to have no fluidity is used. The electrolyte layer is a conductor of ions during the operation of the thermal battery, and at the same time, acts as a separator for the positive electrode and the negative electrode.

As the exothermic agent, a molded product of a mixture of iron powder and potassium perchlorate is used by being alternately laminated with cells. When the heating agent is ignited when the battery is activated, it causes an oxidation-reduction reaction to generate heat and heats the inside of the battery to the operating temperature.
This exothermic agent contains iron in excess of the amount required for the exothermic reaction, has high conductivity even after the exothermic reaction, and acts as a connecting body between adjacent unit cells.

An ignition ball is generally used as a means for activating a thermal battery. When a thermal battery is used, it can be ignited by energizing an ignition ball built into the thermal battery from an external power source to ignite a heat generating agent. It can also be activated by a percussion primer that is ignited by the impact of a hammer. This system does not require an external power source and can activate the thermal battery by mechanical action.

Problems to be Solved by the Invention Thermal batteries are storage-type batteries that can instantly obtain electric power when needed, and because of their high reliability, their applications and usages are on an increasing trend. , Higher capacity,
What can be discharged for a long time is required. However, it is difficult to manufacture a large-area cell due to structural restrictions, and a plurality of power generation block laminates that are electrically connected in parallel are used for high capacity and high output applications.

The discharge capacity of a thermal battery is limited by the discharge capacity of the active material as well as the operating temperature within the battery. Therefore, in designing a thermal battery, it is necessary to optimize not only the amount of active material used but also the method of heat insulation. The inside of the thermal battery is heated uniformly at the time of activation, but with the passage of time, a temperature distribution occurs in which the central portion is high and the surrounding area is low. The long-term thermal battery has a limited discharge life due to the temperature drop of the cells at both ends. In order to design a thermal battery with a long discharge time, it is necessary to prevent the temperature drop of the cells at both ends, but if many heat insulators are used for that purpose, the volume efficiency is lowered.

Means for Solving the Problems The present invention provides a thermal battery that can be discharged for a long time without increasing the number of heat insulators for keeping heat, and is composed of three or more sets of power generation blocks electrically connected in parallel. , In a thermal battery in which these power generation blocks are stacked in the same container,
The number of laminated cells of the power generation blocks at both ends is larger than the number of laminated cells of the inner power generation blocks.

Action The present invention focuses on changes in the temperature distribution inside the thermal battery after activation. After the thermal battery is activated, the temperature gradually decreases from both ends of the laminate with the lapse of time, and the temperature decrease in the central portion is the slowest. That is, even after the temperature at both ends of the power generation block laminate has dropped below the operating temperature,
The central part is still hot and can be discharged. Therefore, discharge the power generation blocks at both ends first,
If the inner power generation block is discharged later, it is possible to discharge for a long time without increasing the heat insulating body for heat retention.

In the battery of the present invention, since the number of stacked cells in the power generation blocks at both ends is large, the discharge voltage is high, and the power generation block inside is preferentially discharged, and the discharge is completed first. Although the discharge rate of the inner power generation block is small in the initial stage, the discharge capability of the power generation blocks at both ends decreases, and the discharge current rate increases as the terminal voltage decreases. The discharge of the power generation blocks at both ends is completed before the temperature of the power generation blocks at both ends becomes equal to or lower than the operating temperature, and thereafter, the discharge of the power generation blocks inside is continued. Since the heat retaining time of the power generation blocks at both ends may be short, it is possible to reduce the number of heat insulators, and it is possible to downsize the thermal battery.

Conventionally, the number of cells of the power generation block has been the same at both ends and center. Therefore, the power generation blocks having the parallel configuration were discharged at the same rate, and the power generation blocks at both ends could not be discharged although the active material remained due to the temperature decrease. In addition, since the inner power generation block was also discharged at the same rate, the discharge ended early despite the temperature state where discharge was possible.

In a general battery system, it is unthinkable to connect laminated cells having different numbers of laminated cells, that is, different voltages, in parallel. However, in the thermal battery, since the molten salt is used as the electrolyte, there is almost no electrical conductivity before activation, and self-discharge does not occur during storage. In addition, since the load is activated with the load connected to the terminals during activation, it is always discharged to the outside when activated, making it difficult for self-discharge due to discharge and charging between internal power generation blocks. is there. That is, if the open circuit voltage of the inner power generation block is equal to or higher than the discharge voltage of the power generation blocks at both ends, there is no problem at all. However, when the number of stacked cells is small or the discharge current is small, the inner power generation block may be temporarily charged by the current of the power generation blocks at both ends at the initial stage of discharging. Therefore,
In this case, the use of rechargeable electrodes such as lithium alloys is preferred.

Generally, it is preferable to increase the number of cells in the power generation blocks at both ends by 1 cell with respect to the number of cells in the power generation block on the inside of 7 cells or more. However, if a rechargeable electrode system such as the iron disulfide / lithium alloy system is used, 1 for every 5 cells
No problem occurred even if the number of cells was increased.

Examples Hereinafter, the present invention will be described using preferred examples.

FIG. 1 is a sectional view of a thermal battery having a configuration in which a plurality of power generation blocks are electrically connected in parallel. 1, 2, 3, and 4 are power generation blocks in which a plurality of cells and heat generating agents are alternately laminated,
1, 4 are power generation blocks at both ends, and 2 and 3 are power generation blocks inside. The number of cells of the power generation blocks at both ends is larger than the number of cells of the power generation blocks inside, and the power generation blocks are electrically connected in parallel with each other. Reference numeral 5 is a connection lead wire on the positive electrode side, and 6 is a connection lead wire on the negative electrode side. In order to simplify the wiring, the power generation blocks are arranged so that the same poles face each other. Reference numeral 7 denotes an explosive charge provided on the central axis of the power generation block for transmitting the ignition energy of the ignition ball 8 to the heat generating agent in the power generation block. Reference numeral 9 denotes an ignition terminal, which can ignite the ignition ball 8 by passing an ignition current from an external power supply. Reference numerals 10 and 11 denote a positive electrode terminal and a negative electrode terminal for taking out an electric current. Reference numeral 12 is a container of the thermal battery, and the inside thereof is filled with a heat insulator 13 for keeping the thermal battery warm.

FIG. 2 is a diagram showing a combination of a cell used in a power generation block and a heat generating agent. Reference numeral 14 denotes a cell, which is composed of three layers of a positive electrode active material layer 15, an electrolyte layer 16, and a negative electrode active material layer 17. 18 is a heat generating agent, and 19 is a metal plate for separating the cell and the heat generating agent.

As an example of the present invention, a thermal battery will be described in which four sets of power generation blocks each composed of a disk-shaped cell and a heating agent connected in series are stacked in the same container.

A cell having a diameter of 50 mm was constructed by using iron disulfide as a positive electrode, a lithium-aluminum alloy as a negative electrode, and a mixture of LiCl-KCl eutectic salt and MgO as an electrolyte layer. The active material discharge capacity of this cell is 150 A · sec. The power generation blocks at both ends have a 6-cell serial configuration, and the inner power generation blocks have a 5-cell serial configuration. The power generation blocks are stacked in the same container, but are electrically connected in parallel. The shape of the thermal battery of the example is 58 mm in outer diameter, 70 mm in height, the nominal voltage is 8.8 V, and the capacity is 600 A · sec.

As comparative examples, using the same cells as those of the example, a thermal battery A having a conventional configuration in which all power generation blocks are connected in 5 cells in series and a thermal battery B having a conventional configuration in which all power generation blocks are connected in 6 cells in series are manufactured. . The comparative thermal battery A has an outer shape of 58 mm, a height of 65 mm, a nominal voltage of 8.0 V, and a capacity of 600 A · sec. The battery B of the comparative example has an outer diameter of 58 mm, a height of 75 mm, and a nominal voltage of 9.
At 6V, the capacity is also 600A · sec. The nominal voltage and height differ depending on the number of cells used.

40% up to 85% of the nominal voltage at an ambient temperature of -45 ° C
When discharged at a current of A, the discharge time of the battery of the present invention was 155
Seconds, the discharge time of the comparative battery A was 139 seconds, and the discharge time of the comparative battery B was 141 seconds. Such a difference in discharge time is due to the fact that the active material utilization rate of the power generation blocks at both ends of the comparative example battery was only about 85% of the designed value due to the temperature decrease, whereas the example battery was discharged 100%. Compared in terms of volumetric efficiency, the battery of the present invention has a capacity of 82 wh / l, and the comparative battery A has a capacity of 72 wh.
/ l, Comparative Example Battery B was 76 wh / l, and the battery of the present invention showed the highest value.

EFFECTS OF THE INVENTION As described above, the battery of the present invention is capable of extending the life of a thermal battery having a parallel configuration required for high capacity without increasing the amount of a heat insulator, and lowering the operating temperature A more excellent effect is exhibited in a long-time discharge type thermal battery in which discharge is limited. The number of stacked cells in the power generation block and the number of parallel power generation blocks can be appropriately changed according to the required voltage and discharge capacity of the thermal battery. The discharge voltage of the conventional thermal battery is proportional to the number of series cells in the power generation block, whereas the discharge voltage of the thermal battery of the present invention is proportional to the weighted average of the number of series cells in each power generation block. Conventionally, the discharge voltage of the thermal battery is an integer multiple of the unit cell voltage and is an arithmetic progression, whereas in the present invention, an intermediate multiple voltage can be designed by changing the parallel number of the power generation blocks. .

[Brief description of drawings]

FIG. 1 is a sectional view of a thermal battery having a configuration in which a plurality of power generation blocks are electrically connected in parallel. FIG. 2 is a diagram showing a combination of a cell used in a power generation block and a heat generating agent. 1, 4 ...... Power generation block at both ends 2, 3 ...... Inside power generation block 10 …… Positive electrode terminal 11 …… Negative electrode terminal 14 …… Cell 18 …… Heating agent 19 …… Metal plate

Claims (1)

[Claims] 1. A thermal battery comprising three or more sets of power generation blocks electrically connected in parallel, wherein these power generation blocks are stacked in the same container. A thermal battery characterized in that the number of stacked cells in the block is larger than that of the stacked cells.