JPH03149756A - Thermal battery - Google Patents

Abstract

PURPOSE:To allow discharging for a long period without increasing a heat insulator for heat insulation by making the number of laminated cells of power generating blocks on both ends larger than the number of laminated cells of power generating blocks on the inside. CONSTITUTION:The number of cells of power generating blocks 1 and 4 on both ends is larger than the number of cells of power generating blocks 2 and 3 on the inside, and power generating blocks 1-4 are electrically connected in parallel. Since the number of laminated cells of power generating blocks 1 and 4 on both ends is larger, the discharge voltage is higher, power generating blocks 1 and 4 are more preferentially discharged than power generating blocks 2 and 3 on the inside, and the discharge is completed earlier. The discharge rate of power generating blocks 2 and 3 on the inside is small at the initial stage, but the rate of the discharging current is increased as the discharge capabilities of power generating blocks 1 and 4 on both ends are reduced and the terminal voltage is reduced. The discharge of power generating blocks 1 and 4 on both ends is completed before the temperature of power generating blocks 1 and 4 on both ends becomes the operating temperature or below, and power generating blocks 2 and 3 on the inside are continuously discharged thereafter. A long life is obtained without increasing the quantity of a heat insulator.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a thermal battery that contains a heat generating agent inside the battery and activates the battery by heating the inside of the battery to a high temperature by igniting the heat generating agent when the battery is used. The present invention provides a thermal battery with high energy density that has a high capacity and can be discharged for a long time.

BACKGROUND OF THE INVENTION A thermal battery is a battery that contains a heat generating agent and uses molten salt as an electrolyte. During storage, the electrolyte is a non-conductive solid salt, so the battery remains inactive, but by burning the exothermic agent and heating the inside of the battery to a high temperature, the electrolyte melts and becomes conductive. The battery will be activated.

A thermal battery is a type of storage battery that has almost no self-discharge during storage, can be stored for a long time, and can be activated instantly when needed.

Also, the temperature range is -55 to 100℃! It is a high energy density battery that can be used even under ambient environmental temperatures. Since thermal batteries in an inactive state have a high internal resistance, they can be incorporated into equipment with a load connected to their terminals. Because of these many features, thermal batteries have become indispensable as power sources for flying objects such as missiles and rockets, and as power sources for various emergencies.

Conventionally, systems using calcium for the negative electrode and calcium chromate for the positive electrode have been used as active materials for this type of thermal battery, but for higher capacity and higher output, lithium or lithium alloys have been used for the negative electrode and lithium alloy for the positive electrode. Thermal batteries using sulfides have been developed intermittently.

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

Pig disulfide, which has high heat resistance, is mostly used as the sulfide in the positive electrode active material, but sulfides of nickel, chromium, cobalt, copper, tungsten, molybdenum, etc., and the Chevrel phase containing these metals are also used. sulfides can also be used.

As the electrolyte, a eutectic salt containing 59 mol % of LiCl and 41 mol % of Cl 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. The electrolyte used is lithium for the negative electrode mixed with insulating powder such as magnesium oxide, boron oxide, or zirconium oxide, which has corrosion resistance, to eliminate fluidity. The electrolyte layer is an ion conductor during thermal battery operation, and at the same time acts as a separator between the positive and negative electrodes.

As the exothermic agent, a molded mixture of iron powder and potassium perchlorate folate is used by laminating the cells alternately. When the exothermic agent is ignited during battery activation, it causes an oxidation-reduction reaction and generates heat, heating 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 also acts as a connector between adjacent cells.

Ignition balls are commonly used as a means of activating thermal batteries. When the thermal battery is used, an external power supply energizes the ignition ball built into the thermal battery to ignite the heat generating agent. It can also be activated by a percussion tube that is ignited by a hammer blow. This method does not require an external power source, and the thermal battery can be activated by mechanical action.

Thermal batteries are storage type batteries that can obtain power instantaneously when needed, and because they have high reliability, their applications and usage are increasing rapidly. There is a demand for higher capacity and longer discharge time. However, it is difficult to manufacture large-area cells due to structural constraints, and for high-capacity, high-output applications, a stack of multiple power generation blocks electrically connected in parallel is used.

The discharge capacity of a thermal battery is limited not only by the discharge capacity of the active material but also by the operating temperature within the battery.

For this reason, thermal battery design is not only based on the amount of active material used;
The heat insulation method must also be optimized.The inside of a thermal battery is heated uniformly during activation, but as time passes, a temperature distribution develops in which the temperature is higher in the center and lower at the periphery. .

The discharge life of a thermal battery that discharges for a long time is limited by 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 of the cells at both ends from dropping, but if a large number of insulators are used for this purpose, this results in a decrease in volumetric efficiency.

Means for Solving the Problems The present invention has a length of 11 r without increasing the number of heat insulators for heat retention.
It provides a thermal battery capable of rA discharge, and consists of more than 381 power generation blocks each electrically connected in parallel.
A thermal battery in which these power generating units are laminated in the same container is characterized in that the number of stacked cells in the power generating blocks at both ends is greater than the number of stacked cells in the inner power generating block.

Function The present invention focuses on changes in temperature distribution inside a thermal battery after activation. After activating the thermal battery, the temperature gradually decreases from both ends of the stack as time passes, and the temperature decrease at the center is the slowest. That is, even after the temperature at both ends of the power generation block laminate falls below the operating temperature, the central portion remains at a high temperature and discharge is possible.

Therefore, by discharging the power generating blocks at both ends first and discharging the inner power generating blocks later, it is possible to discharge for a long time without increasing the number of heat insulators.

In the battery of the present invention, since the power generation blocks at both ends have a large number of laminated cells, the discharge voltage is high, and the power generation blocks on the inside are discharged preferentially, and the discharge ends first. Initially, the discharge rate of the inner power generation block is small, but as the discharge capacity of the power generation blocks at both ends decreases and the terminal voltage decreases, the discharge current rate increases. Discharging of the power generating blocks at both ends is completed until the temperature of the power generating blocks at both ends becomes equal to or lower than the operating temperature, and thereafter the inner power generating block continues discharging. Since the heat retention time of the power generation blocks at both ends may be short, the number of heat insulators can be reduced, and the thermal battery can be made smaller.

Conventionally, power generation blocks had the same number of cells at both the ends and the center. As a result, the power generation blocks in the parallel configuration proceeded to discharge at the same rate, and the power generation blocks at both ends were unable to discharge due to temperature drop, even though active material remained. In addition, because the inner power generation block was also discharging at the same rate, the discharging ended early even though the temperature was such that it could be discharged.

In a general battery system, it is unthinkable to connect stacked cells with different numbers of stacked cells, that is, stacked cells with different voltages in parallel. However, in thermal batteries, since molten salt is used as an electrolyte, there is almost no electrical conductivity before activation, and self-discharge does not occur during storage. In addition, since it is activated with the load connected to the terminal, it is always in a state of discharge to the outside during activation, and self-discharge due to discharging and charging between internal power generation blocks is unlikely to occur4. 'R state. That is, there is no problem at all as long as the voltage across the inner power generation block is equal to or higher than the discharge voltage of the power generation blocks at both ends.

However, when the number of laminated 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 beginning of discharge. Therefore, the use of rechargeable electrodes such as lithium alloys is preferred in this case.

In general, it is preferable to increase the number of cells in the power generation blocks at both ends by one cell for each cell number in the inner power generation block equal to or greater than the cell number in the inner power generation block.However, when using a rechargeable electrode system such as an iron disulfide/lithium alloy system, No problem occurred even when one cell was increased for every five cells.

Example The present invention will be explained below using preferred embodiments.

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. 1.2.3.4 is a power generation block in which multiple cells and exothermic agents are alternately stacked.
．． 4 is a power generation block at both ends, and 2.3 is an inner power generation block. The number of cells in the power generation blocks at both ends is greater than the number of cells in the power generation blocks on the inside, and each power generation block is electrically connected to each other in parallel. 5 is a connection lead wire on the positive electrode side, and 6 is a connection lead wire on the negative electrode side. To simplify wiring, each power generation block is arranged so that the same poles face each other. Reference numeral 7 denotes a fuse provided on the center axis of the power generation block, which transmits the ignition energy of the ignition ball 8 to the exothermic agent inside the power generation block. 9 is a terminal for ignition, by which the ignition ball 8 can be ignited by passing an ignition current from an external power source; 10.11 is a positive terminal and a negative terminal for taking out the current. 12 is a container for 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 the combination of cells and exothermic agents used in the power generation block. 14 is a cell, positive electrode active material Fj15
, an electrolyte layer 16, and a negative electrode active material layer 17. 1B is a heat generating agent, and 19 is a metal plate separating the cell and the heat generating agent.

As an embodiment of the present invention, a power generation block consisting of a disc-shaped cell and a heat generating agent connected in series is housed in a container for 48 hours.
A single-layer thermal battery will be explained.

Iron disulfide is used for the positive electrode, lithium-aluminum alloy is used for the negative electrode, and iCl-KCI eutectic salt and M are used as the electrolyte layer.
A cell of diameter 50+w+n was constructed using a mixture of 2O. The active material discharge capacity of this cell is 150 A·sec.

The power generation blocks at both ends have a 6-cell series configuration, and the inner power generation block has a 5-cell series configuration. Although the power generation blocks are stacked in the same container, they are electrically connected in parallel. The shape of the example thermal battery is an outer diameter of 5B++++n
, height 70++uw, nominal voltage 8.8V, capacity 60
It is 0A・sec.

As a comparative example, a thermal battery A with a conventional configuration in which all power generation blocks were connected in series with 5 cells and a thermal battery B with a conventional configuration in which all power generation blocks were connected in series with 6 cells were created using the same cells as in the example. . Comparative example thermal battery A has an outer diameter of 58s+
m-height 6511ml, nominal voltage 8. Ov has a capacity of 6
00A・sec. Comparative Example Battery B has an outer diameter of 58 m.
m, height 751II+, the nominal voltage is 9.6v, and the capacity is the same < 600A·s. Difference in the number of cells used [
This is why the nominal voltage and height are different.

When the battery of the present invention was discharged at a current of 40^ to a voltage of 85% of the nominal voltage at an environmental temperature of -45°C, the discharge time of the battery of the present invention was 155 seconds, and the discharge time of Comparative Example Battery A was 139 seconds. jt! ! The discharge time of B was 141 seconds. This 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 around 85% of the designed value due to the temperature drop, whereas the example battery was 100% discharged. Comparing the volumetric efficiency, the battery of the present invention has a volumetric efficiency of 82vb/
Comparative Example Battery A had a value of 72w11/1, Comparative Example Battery B had a value of 76w11/1, and the battery of the present invention showed the highest value.

Effects of the Invention As mentioned above, the battery of the present invention is capable of extending the life of thermal batteries in a parallel configuration, which is necessary for increasing capacity, without increasing the amount of heat insulating material, and by lowering the operating temperature. More excellent effects are exhibited in long-duration discharge type thermal batteries where discharge is limited. The number of laminated cells in a power generation block and the number of parallel power generation blocks can be changed as appropriate depending on the required voltage and discharge capacity of the thermal battery. While the discharge voltage of conventional thermal batteries is proportional to the number of cells in series in a power generation block, the discharge voltage of the thermal battery of the present invention is proportional to the weighted average of the number of cells in series in each power generation block. Conventionally, the discharge voltage of thermal batteries was an integer multiple of the voltage of the unit cell, which was an arithmetic progression, but in the present invention, by changing the number of power generation blocks in parallel, it is possible to design voltages in the middle of integer multiples. .

[Brief explanation of the drawing]

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 the combination of cells and exothermic agents used in the power generation block. 1, 4...Power generation blocks at both ends 2.3...Inner power generation block 10...Positive electrode terminal 11...Negative electrode terminal 14...Cell 18...Heat generating agent 19...・・Metal plate

Claims (1)

[Claims] 1. In a thermal battery that consists of three or more sets of power generation blocks each electrically connected in parallel and these power generation blocks are stacked in the same container, the number of stacked cells of the power generation blocks at both ends is equal to the number of stacked cells of the inner power generation blocks. A thermal battery characterized by having more cells than cells.