JP2005129277A - Thermal battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal battery by which discharge can be carried out for a long time compared with a conventional thermal battery. <P>SOLUTION: As for the thermal battery provided with (a) at least one unit cell provided with a positive electrode, a negative electrode and an electrolyte layer arranged between the positive electrode and the negative electrode, (b) an exothermic agent to melt an electrolyte contained in the electrolyte layer, (c) a means to ignite an exothermic agent, and (d) the unit cell, the exothermic agent, and an exterior case to house the means, LiNO<SB>3</SB>of which the melting point is lower than a conventional one is used as the electrolyte. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a thermal battery, and more particularly to a thermal battery having an improved electrolyte.

  A thermal battery is a battery that generates a voltage by heating the inside of the battery to a high temperature to melt the electrolyte. A heating agent is used for heating the inside of the battery. When the temperature inside the battery rises to around 600 ° C. due to the heat generating agent, the electrolyte melts. Thereafter, the battery is allowed to cool and the temperature inside the battery is lowered, but can be discharged if the temperature is about 100 to 120 ° C. higher than the melting point of the electrolyte.

  Conventionally, LiCl-KCl eutectic salt has been used as the main material of the electrolyte of the thermal battery. The melting point of the LiCl—KCl eutectic salt is about 350 ° C. Therefore, a thermal battery using LiCl—KCl eutectic salt as an electrolyte can be used in a temperature range of 470 ° C. to 600 ° C.

  With the recent enhancement of performance of defense equipment, there is a demand for extending the life (discharging over a long period) of the thermal battery used. However, as described above, in the electrolyte made of the conventional LiCl—KCl eutectic salt, the usable temperature range is in the range of 470 ° C. to 600 ° C., so the temperature in the battery is maintained at 470 ° C. or higher. Only during that time can the battery be discharged.

On the other hand, instead of LiCl-KCl eutectic salt, KBr-LiBr-LiCl eutectic salt, LiBr-KBr-LiF eutectic salt, or LiBr-LiCl-LiF eutectic salt is used as the electrolyte used in the thermal battery. Has been proposed (see Patent Document 1). However, this proposal is made to improve the discharge characteristics and is not intended to extend the life of the thermal battery.
Japanese Patent Laid-Open No. 3-119661

  An object of the present invention is to obtain a thermal battery capable of extending a temperature range in which the voltage of the thermal battery can be generated, and thereby discharging for a long time.

The thermal battery of the present invention has a main feature in that an electrolyte in a molten state in a wide temperature range, that is, an electrolyte having a melting point lower than that of a conventional electrolyte is used. That is, the thermal battery of the present invention is
(A) at least one unit cell comprising a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode;
(B) a heat generating agent for melting the electrolyte contained in the electrolyte layer;
(C) means for igniting the exothermic agent, and (d) the unit cell, the exothermic agent, and an outer case that houses the means,
And LiNO ₃ as the electrolyte.

  In the above thermal battery, the electrolyte layer preferably contains MgO as a binder.

  By using lithium nitrate having a low melting point as the electrolyte, it is possible to provide a thermal battery having a long dischargeable time as compared with a conventional thermal battery. Further, since lithium nitrate is used, the amount of Li in the electrolyte layer is increased as compared with the conventional one, and the conductivity of the electrolyte layer can be improved. As a result, the discharge characteristics of the thermal battery are also enhanced.

The thermal battery of the present invention will be described with reference to FIG.
FIG. 1 is a perspective view in which a part of a thermal battery according to an embodiment of the present invention is cut away.

The structure of the thermal battery of the present invention is basically the same as the conventional one, and as shown in FIG. 1, it has a laminated body in which unit cells 7 and heating agent layers 5 are alternately stacked. An igniting agent layer 4, an igniter 3 and a terminal 2 are disposed at the upper end of the laminated body, and a igniting belt 6 and a lead plate 8 are attached around the laminated body. Such a laminate is housed in an outer case 1 whose inner surface is covered with a heat insulating material 9, and the opening of the outer case 1 is sealed with a battery lid 10.
In this embodiment, the igniter 3, the igniting agent layer 4, and the igniting zone 6 function as a means 11 for igniting the heat generating agent.

  In this thermal battery, when a start signal is applied to the terminal 2, the igniter 3 is combusted, and then the igniter layer 4 and the igniter zone 6 are combusted and the heat generating agent layer 5 is ignited. Thereby, the exothermic agent burns and the unit cell 7 is heated. And when the electrolyte (not shown) contained in the unit cell 7 melts, it becomes an ionic conductor and discharge becomes possible.

  For the outer case 1, the terminal 2, the igniter 3, the igniting agent layer 4, the heat generating agent layer 5, the igniting zone 6, the lead plate 8, the heat insulating material 9, and the battery lid 10, use those known in the art. Can do.

The unit cell 7 includes a negative electrode, a positive electrode, and an electrolyte layer disposed between the negative electrode and the positive electrode.
In the thermal battery of the present invention, as the negative electrode, lithium fixed with iron powder, lithium aluminum alloy, lithium silicon alloy, or the like can be used.
As the positive electrode, one made of a mixture of iron disulfide and an electrolyte can be used.

  In the thermal battery of the present invention, the electrolyte contained in the electrolyte layer is made of lithium nitrate. Lithium nitrate has a melting point of about 260 ° C., and has a melting point as low as about 100 ° C. as compared with a LiCl—KCl eutectic salt conventionally used as an electrolyte.

  Usually, the internal temperature of the thermal battery rises to around 600 ° C. due to combustion of the built-in heat generating agent. However, after the exothermic agent is combusted, the internal temperature of the thermal battery gradually decreases due to cooling.

  As described above, the conventional thermal battery using the LiCl-KCl eutectic salt as an electrolyte increases the internal resistance of the electrolyte layer when the internal temperature becomes lower than 470 ° C., so that the voltage drops rapidly and operates as a battery. It becomes difficult to do.

  On the other hand, in the present invention, since the melting point of lithium nitrate is about 260 ° C., a voltage can be generated and discharged until the internal temperature of the thermal battery reaches about 350 ° C.

  Next, FIG. 2 shows the time change of the internal temperature of the thermal battery due to cooling. According to FIG. 2, the time for maintaining 350 ° C. or higher is longer than the time t for maintaining the temperature inside the thermal battery of 470 ° C. or higher, which is about 1.2 times. Thereby, it is understood that the thermal battery of the present invention can be discharged for a long time as compared with the conventional one.

  Furthermore, by using an electrolyte made of lithium nitrate, the amount of lithium in the electrolyte layer is increased as compared with a conventional thermal battery using LiCl—KCl eutectic salt as an electrolyte. For this reason, the internal resistance of the thermal battery can be reduced, and as a result, the discharge characteristics of the thermal battery can be improved.

  The electrolyte layer preferably contains magnesium oxide (MgO) as a binder in order to suppress the flow of the molten electrolyte. Magnesium oxide is preferably contained in an amount of 35 to 60% by weight of the electrolyte layer. When the added amount of magnesium oxide is 35% by weight or more, the effect of suppressing the internal short circuit of the battery is further improved by being retained in the electrolyte layer so that the molten salt does not spill. Moreover, by making the addition amount 60% by weight or less, the internal resistance can be lowered and the discharge characteristics can be further improved.

Further, in order to increase the stability of the electrolyte in the low temperature region and the high temperature region, it is preferable to use lithium nitrate mixed with a substance other than lithium nitrate as the electrolyte. As other substances, nitrates other than lithium nitrate (for example, NaNO ₃ , KNO _3, etc.), LiCl, KCl, LiCl—KCl eutectic salt, and the like can be used.

When the nitrate other than lithium nitrate such as NaNO ₃ , KNO ₃ or the like is used as the other substance, the amount added is preferably in the range of 10% to 50% by weight of the electrolyte layer. By making the addition amount 10% by weight or more, the stability of the electrolyte can be further increased. Moreover, the discharge characteristic in low temperature can be improved by making addition amount into 50 weight% or less.

  When LiCl—KCl eutectic salt is used as the other substance, the proportion of LiCl—KCl eutectic salt in the electrolyte is preferably 50% by weight or less in order to improve discharge characteristics at a lower temperature. .

  A unit cell with a diameter of 37 mm was prepared using iron disulfide as the positive electrode active material and lithium as the negative electrode active material, and the discharge characteristics were evaluated.

As the positive electrode, a molded product of a mixture (0.9 g) composed of FeS ₂ (70% by weight) and a LiCl—KCl-based electrolyte (30% by weight) was used. As the negative electrode, 0.1 g of Li metal was adsorbed on 1.5 g of iron powder and then molded. As the electrolyte layer, a molded product (0.8 g) obtained by adding 20% by volume of MgO powder, which is a binder for eliminating fluidity, to LiNO ₃ was used.

  A unit cell was fabricated by laminating the positive electrode, the electrolyte layer, and the negative electrode as described above. The unit cell was sandwiched between two hot plates in an argon atmosphere and discharged at a constant current of 1 A, and the voltage change with time was measured. The measurement was performed when the temperature of the unit cell was 470 ° C and 350 ° C. The obtained results are shown in FIG. Here, a curve B represents a voltage change when measured at 470 ° C., and a curve C represents a voltage change when measured at 350 ° C.

Comparative Example 1

  As the electrolyte layer, in the same manner as in Example 1, except that LiCl—KCl eutectic salt (LiCl: 59 mol%, KCl: 41 mol%) mixed with 20 vol% of MgO as a binder was used. A comparative unit cell was produced. Using the obtained comparative unit cell, the voltage change with time was measured at 470 ° C. in the same manner as in Example 1. The obtained result is shown in FIG. 3 (curve A). In this comparative unit cell, when the temperature is lower than 470 ° C., the internal resistance of the electrolyte layer is increased and the discharge cannot be performed. Therefore, the discharge characteristics at 350 ° C. are not measured.

As shown in FIG. 3, when the measurement temperature is 350 ° C., the unit cell according to the present invention can be discharged, whereas the conventional battery cannot be discharged.
Furthermore, when the measurement results at 470 ° C. are compared, it is found that the voltage is high in the unit cell according to the present invention. This is because, in the present invention, since lithium nitrate is used as the electrolyte, not the conventional LiCl—KCl eutectic salt, the amount of Li in the electrolyte layer increases and the internal resistance of the electrolyte layer decreases. . Thus, according to the present invention, the discharge characteristics of the thermal battery can also be improved.

In addition, although the results are not shown, even when LiNO ₃ mixed with nitrate such as NaNO ₃ or KNO _{3 in} the range of 10 wt% to 50 wt% is used as the electrolyte, the conventional thermal battery Compared with, it is possible to extend the life of the thermal battery.
The same applies when LiCl—KCl eutectic salt is mixed with lithium nitrate in the range of 10 wt% to 50 wt%.

  According to the present invention, it is possible to provide a thermal battery that can be discharged for a long time and has improved discharge characteristics as compared with a conventional battery.

It is the perspective view which notched some thermal batteries concerning one embodiment of the present invention. It is a graph which shows the time change of the internal temperature of a thermal battery by standing_to_cool. It is a graph which shows the time change of the voltage when a unit cell is discharged with the constant current of 1A in 350 degreeC or 470 degreeC.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exterior case 2 Terminal 3 Igniter 4 Ignition agent layer 5 Heat generating agent layer 6 Heat conduction zone 7 Unit cell 8 Lead plate 9 Heat insulating material 10 Battery cover 11 Means to ignite the heating agent

Claims (2)

(A) at least one unit cell comprising a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode;
(B) a heat generating agent for melting the electrolyte contained in the electrolyte layer;
(C) means for igniting the heat generating agent, and (d) an exterior case that houses the unit cell, the heat generating agent, and the heat generating means,
A thermal battery comprising:
A thermal battery comprising LiNO ₃ as the electrolyte.   Furthermore, the thermal battery of Claim 1 in which MgO is contained in the said electrolyte layer as a binder.

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