JPH0740489B2 - 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 built in the battery and the heating agent is ignited when the battery is used to heat the inside of the battery to a high temperature to activate the battery. The present invention provides a thermal battery having excellent discharge characteristics and a long storage life.

Conventional technology A thermal battery is a battery that uses molten salt as an electrolyte, and since the electrolyte is a non-conductive solid salt during storage, it is in an inactive state as a battery, but the built-in heating agent burns. Then, by heating the inside of the battery to a high temperature, the electrolyte is melted and becomes conductive, 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 supplies for missiles, rockets, and other flying vehicles, and various emergency power supplies.

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 higher output, lithium or lithium alloy is used for the negative electrode. Thermal batteries using sulfides have been developed.

Lithium for the negative electrode is an excellent metal that is lightweight and has a high electromotive force, but since it has a low melting point of 179 ° C and melts at the operating temperature of a thermal battery, it is impregnated and held in a porous body of iron or nickel, or metal powder. It is used by mixing it with the one that loses fluidity. Further, lithium is easy to form an alloy, and an alloy with boron, aluminum, silicon, gallium, germanium or the like can be used as the negative electrode.

As the sulfide of the positive electrode active material, iron disulfide, which has high heat resistance, is used exclusively, 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, LiCl-59 mol% and KCl-41 mol% eutectic salts are 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 one in which lithium as the negative electrode is mixed with an insulating powder such as magnesium oxide, boron nitride, or zirconium oxide having corrosion resistance so as to have no fluidity. During the operation of the thermal battery, the electrolyte layer acts as a separator for the positive electrode and the negative electrode at the same time as the ionic conductor.

As a heat generating agent, a molded product of a mixture of iron powder and potassium perchlorate is used by alternately stacking it with a unit cell (hereinafter simply referred to as a cell). 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 cells.

A material obtained by adhering a mixture of zirconium and barium chromate to an inorganic fiber is also used as an exothermic agent. However, since this heat generating agent has low conductivity, a metal plate for connecting the cells is required.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In recent years, there has been a demand for higher capacity and higher power thermal batteries, and it has become impossible to meet the demand with conventional LiCl—KCl eutectic salt electrolytes.

LiCl-KCl eutectic salt is a mixture of LiCl-59 mol% and KCl-41 mol%, which has a low concentration of lithium ions in the molten state and a low lithium ion transport number. When discharged with a large current exceeding 1 A / cm ² per area, the amount of lithium ions generated by the discharge exceeds the amount of movement of lithium ions in the electrolyte, increasing the lithium ion concentration around the negative electrode, The composition of the electrolyte changes. When the discharge is further continued, excess lithium ions are deposited in the vicinity of the negative electrode as solid LiCl, and the conductivity of the ions decreases, so that the internal resistance increases and the discharge cannot be continued.

As a result of examining various molten salt systems instead of LiCl-KCl system, KB
r-LiBr-LiCl system, LiBr-KBr-LiF system, LiBr-LiCl-LiF system 3
The excellent discharge characteristics of the molten salt electrolyte composed of the component system were revealed. Each of these electrolytes has a high concentration of lithium ions and the diffusion of lithium ions is fast, so that a concentration gradient is unlikely to occur, and a large current discharge is possible.

However, these molten salt systems have high electrical conductivity at room temperature and cannot be used as electrolytes for thermal batteries.

One of the features of thermal batteries is that the internal resistance when unused is 1000 MΩ
It is as high as the above, there is almost no self-discharge during storage, and it can be stored for more than 10 years. However, the internal resistance of a thermal battery using an electrolyte composed of a three-component system at room temperature was as low as 10 to 500 MΩ, and storage for a long period of time was impossible. Even in the inactive state at room temperature, when the device was connected and left to stand, discharge gradually proceeded and the capacity decreased.

The conductivity of LiCl-KCl eutectic salt at room temperature is 10 ^-10 Scm- ¹ or less, and the conductivity of the electrolyte layer powder-molded by mixing magnesium oxide is 10 ^{-11 Scm} - ¹ or less. .

On the other hand, it was found that the electric conductivity of the electrolyte layer using the ternary molten salt at room temperature was as high as 10 ^-9 S · cm ⁻¹ or more. These have a conductivity of 2 ×, which is one of the constituents of LiBr.
It seems that it is as high as 10 ^-9 S · cm ^-1 . Further, in the ternary system, there is a possibility that the number of vacancies for ionic conduction is increased due to the increase of Schottky defects due to the mixed ion effect.

The conventionally used LiCl-KCl eutectic salt has a drawback in that it does not discharge a large amount of self-discharge, but cannot discharge a large amount of current, and a ternary electrolyte capable of discharging a large amount of electric current has a large amount of self-discharge.

Means for Solving the Problems The present invention is that the increase in internal resistance in large current discharge of a thermal battery using LiCl-KCl eutectic salt as an electrolyte is biased near the negative electrode, and the increase in resistance near the positive electrode is observed. Guided by discovering that it is not done. That is, it was shown that a large current can be discharged by changing the electrolyte in the vicinity of the negative electrode to an optimum one.

The present invention relates to a thermal battery in which a cell layer composed of a positive electrode active material layer, an electrolyte layer and a negative electrode active material layer, and a heat generating agent layer are laminated, wherein the electrolyte layer is a positive electrode side first electrolyte layer and a negative electrode side. The present invention provides a thermal battery comprising two layers of the second electrolyte layer, wherein the components of the first electrolyte layer and the second electrolyte layer are different.

Effect of the Invention By using two layers of electrolyte layers, it is possible to share and maintain the properties required for each layer, less self-discharge during storage, and possible thermal battery capable of large current discharge. It was

An electrolyte layer suitable for discharging the positive electrode can be used on the positive electrode side, and an electrolyte layer preferable for discharging the negative electrode can be used on the negative electrode side. It is sufficient for one of the electrolyte layers to have high resistance at room temperature, that is, at least one of the first and second electrolyte layers has a conductivity at room temperature of 10 ^-10 S.
・ It must be below cm ^-1 .

The first electrolyte layer in contact with the positive electrode preferably has a composition effective in improving the utilization rate of the positive electrode. Conventionally used LiCl-KCl
The eutectic salt has a low melting point, is inexpensive, and has a high utilization factor of the positive electrode. Therefore, it is an optimum component for the first electrolyte layer.

The second electrolyte layer in contact with the negative electrode preferably has a composition effective in improving the utilization rate of the negative electrode. The composition of the three-component electrolyte that is effective in improving the utilization rate of the negative electrode is as follows.

KBr-LiBr-LiCl system KBr-38 mol%, LiBr-37 mol%, LiCl-25 mol% LiBr-KBr-LiF system LiBr-63.5 mol%, KBr-34.0 mol%, LiF-2.5 mol% LiBr-LiCl- LiF-based LiBr-47 mol%, LiCl-31 mol%, LiF-22 mol% Examples Hereinafter, the constitution of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a cell used in the thermal battery of the present invention. 1
Is a positive electrode layer and 2 is a negative electrode layer. Reference numeral 3 is a first electrolyte layer on the positive electrode side, and 4 is a second electrolyte layer on the negative electrode side, the components of which are different. Although the cell of the present invention is composed of four layers, each layer may be formed as a single layer and then combined, or those composed of two or more layers may be combined.

FIG. 2 is a sectional view of a conventional cell. It is composed of three layers of a positive electrode layer 1 ', an electrolyte layer 5 and a negative electrode layer 3', and the electrolyte layer is a single layer.

FIG. 4 is a sectional view of the thermal battery of the present invention. Reference numeral 6 denotes a laminated cell, which is composed of four layers of a positive electrode layer, two electrolyte layers, and a negative electrode layer. Reference numeral 5 is an exothermic agent layer laminated alternately with the cells 6. Reference numeral 8 is a charge detonating agent filled in the central hole of the laminate. Reference numeral 9 denotes an ignition ball which instantly ignites when an ignition current is applied to the ignition terminal 10, ignites the charge 8 and ignites a flame to ignite the heat generating agent 7 of the laminated body to activate the thermal battery. Be converted. Reference numeral 11 is a positive electrode terminal, and 12 is a negative electrode terminal. Reference numeral 13 is a heat insulating material for insulating and keeping the inside of the thermal battery, and 14 is a battery container.

Example 1 A single cell test was conducted by constructing a thermal battery cell having a diameter of 24 mm by using iron disulfide as the positive electrode and a lithium aluminum alloy as the negative electrode. 0.5 g of a mixture of 70% FeS _{2 and} 30% of LiCl—KCl-based electrolyte was used as the positive electrode, and 0.3 g of LiAl alloy powder was used as the negative electrode. For the electrolyte layer, a powder raw material containing 20% by volume of MgO powder in order to eliminate fluidity was used, and the thickness after molding was 0.4 mm in each case. The test cell was sandwiched between two hot plates in an atmosphere of argon, and the temperature of the cell was maintained at 470 ° C. to discharge at a current of 1.22 A / cm ² .

Table 1 shows the composition of the electrolyte layer used for each test cell, the insulation resistance of the test cell, and the discharge time up to a discharge voltage of 1.4V. The cells with symbols A, B, C, and D are conventional comparative examples including a single electrolyte layer, E, F, and G are comparative examples including two electrolyte layers, and H, I, and J are two-layer electrolyte layers. 3 is an example of the present invention consisting of layers.

In the conventional example A, the insulation resistance is high, but the discharge time is short. Also,
B, C, and D have a drawback that the discharge time is long, but the insulation resistance is low. E, F, and G using the two electrolyte layers are those using a LiCl-KCl eutectic salt as the electrolyte layer 2 on the negative electrode side, and the insulation resistance is greatly improved, but the discharge time is not extended much. Even with this configuration, if the operating temperature is high, LiCl-K
It has been confirmed that the discharge time is longer than in the case of a Cl-based electrolyte single layer. It can be seen that H, I, and J having the two-layer electrolyte structure have high insulation resistance and a long discharge time. This is the most preferable configuration.

FIG. 3 shows the change in discharge time when the test temperature was changed for the A, D, G, and J single cell configurations. The discharge time is the shortest for A using a LiCl-KCl-based single-layer electrolyte and the longest for D using a LiBr-LiCl-LiF-based single-layer electrolyte. Bilayer electrolyte cells using the same electrolyte layer showed discharge times in between these. The conventional A has a short discharge time and the conventional D has a low insulation resistance. J of the battery of the present invention has a high insulation resistance and the discharge time is also increased. The G cell, which is a comparative example of the two-layer electrolyte layer, should theoretically show the same tendency as the A cell, but the discharge time was extended as the test temperature was increased. It is considered that the two layers of molten electrolyte were mixed at high temperature.

The results showing the same tendency were obtained for the single-layer and double-layer electrolytes when other three-component electrolytes were used.

Example 2 A thermal battery as shown in FIG. 4 was constructed by using iron disulfide as a positive electrode active material and a lithium aluminum alloy as a negative electrode active material. An LiCl-KCl-based electrolyte solution was used as the first electrolyte layer, and a LiBr-LiCl-LiF-based electrolyte solution was used as the second electrolyte layer. In addition,
The two electrolyte layers had a thickness of 0.4 mm. The cell used had a diameter of 44 mm, and 17 cells were stacked in series. The insulation resistance between terminals was 1000 MΩ or more.

FIG. 5a shows the battery of the present invention activated in a temperature bath of -30 ° C. and discharged at a current of 15 A. b is a conventional battery of a comparative example, which has the same electrode configuration as the battery of the present invention,
The insulation resistance of the conventional battery, which uses a single-layer LiCl-KCl-based electrolyte layer, was 1000 MΩ or more. The battery of the present invention was able to obtain a discharge time twice or more that of the conventional battery without lowering the insulation resistance.

EFFECTS OF THE INVENTION The present invention enables the use of a three-component electrolyte having excellent discharge characteristics without lowering the insulation resistance by using two electrolyte layers, which is of great industrial value. is there.

[Brief description of drawings]

FIG. 1 is a sectional view of a thermal battery cell according to the present invention, FIG. 2 is a sectional view of a conventional thermal battery cell, and FIG. 4 is a sectional view of a thermal battery according to the present invention. FIG. 3 and FIG. 5 show the test results of the example together with the conventional example. DESCRIPTION OF SYMBOLS 1 ... Positive electrode layer 2 ... Negative electrode layer 3 ... 1st electrolyte layer 4 ... 2nd electrolyte layer 6 ... Cell 7 ... Exothermic agent a ... Discharge characteristic b of this invention Example thermal battery b ... Discharge characteristics of conventional thermal battery

Claims (3)

[Claims] 1. A thermal battery in which a cell layer including a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, and a heating agent layer are laminated, wherein the electrolyte layer is a first electrolyte layer on the positive electrode side and a negative electrode. The second electrolyte layer on the side is composed of two layers, the first electrolyte layer is a mixture of LiCl-KCl eutectic salt and an insulator powder, and the second electrolyte layer is a KBr-LiBr-LiCl system. , LiBr-KBr-LiF
System, a thermal battery characterized by being a mixture of one of three-component molten salts consisting of LiBr-LiCl-LiF system and an insulator powder. 2. The thermal battery according to claim 1, wherein the composition of the LiCl-KCl eutectic salt used in the first electrolyte layer is LiCl-59 mol% and KCl-41 mol%. 3. The composition of the ternary molten salt used in the second electrolyte layer is such that in the KBr-LiBr-LiCl system, KBr-38 mol%, LiBr-37 mol%, LiCl-25 mol%, LiBr -In the KBr-LiF system, LiBr-63.5 mol%, KBr-34.
0 mol%, LiF-2.5 mol%, LiBr-LiCl-LiF system, LiBr-47 mol%, LiCl-31
%, And LiF-22 mol%.
The thermal battery described.