JPS6155224B2 - - Google Patents

Description

Detailed Description of the Invention The present invention aims to extend the operating time of a thermal battery containing a heating agent, and more specifically, the present invention aims to extend the operating time of a thermal battery containing a heating agent. This aims to achieve the above objective by improving the heat retention effect.

A thermal battery is a battery that uses molten salt as an electrolyte, which is solid at room temperature but becomes liquid when heated to high temperatures.
A typical electrolyte is LiCl-KCl eutectic mixed salt (43% by weight of LiCl, 57% by weight of KCl, melting point: 352% by weight)
°C) and LiBr-KBr eutectic mixed salt LiBr52% by weight,
KBr48% by weight, melting point 330℃). In thermal batteries, these electrolytes are practically used in an anhydrous state, so they have the advantage of being able to use metals with a high negative electrode potential, such as magnesium and calcium, as negative electrode materials. In addition, it is a battery that has good high-rate discharge characteristics, can withstand long-term storage of 5 years or more, can be used in a wide range of environmental temperatures, and is advantageous when obtaining a large current in a short period of time.

A typical conventional cell structure consists of a metallic calcium plate as a negative electrode, a LiCl-KCl eutectic salt as an electrolyte, calcium chromate as a depolarizer, and iron and nickel as a positive current collector plate. On the other hand, typical examples of heating agents include:
A powder mixture of metal powder and oxidizing agent is used, and a so-called thermite reaction is utilized. Typical examples include Zr-BaCrO ₄ and Zr-PbCrP ₄ -KMnO ₄ , which are selected after comprehensive consideration of calorific value, combustion characteristics, gas generation amount, etc.

Any number of these unit cells and heating agents can be stacked alternately to obtain any voltage, but as mentioned above, in thermal batteries, the electrolyte of the unit cell melts due to the combustion heat of the heating agent. Since the battery can only supply power when the battery is in the active state, how long the activation temperature of the stack is maintained is a very important factor that determines the length of the operating time. In particular, since the unit cells at both ends of the laminate, which have a large heat dissipation area, cool down much faster than the other units at the center, it is necessary to improve the heat retention ability of the unit cells at both ends.

Various proposals have been made and improvements have been made to the conventional thermal insulation layer, but the basic and common idea is that Q=
It is constructed based on the relationship of C・M・t.
That is, by applying the fact that the amount of heat Q is proportional to the product of specific heat C, weight M, and temperature t, the problem was how to efficiently increase Q and slow down the cooling rate. For this reason, there are proposals for C using Li ₂ SO ₄ -NaCl heat storage material, and proposals for M using metal plates such as steel, and since t can be set arbitrarily depending on the amount of heating agent used, these Just make good use of the combination.

However, the conventional way of thinking is to use a heating agent to heat the insulation material to a certain set temperature.
This method relies on natural cooling, and the heat insulating layer itself proposed by the present invention was not designed to generate heat.

The disadvantage of the conventional method is that since the Q must be large, the volume occupied by the heat insulating layer becomes large and the heat insulating layer becomes heavy, which is one of the obstacles to making the device smaller and lighter. In addition, in the case of the above-mentioned metal plate, under environmental conditions such as vibration and shock,
Often the heating agent would fall out and the system would become inoperable.

The present invention provides a thermal battery having a power generation main part in which unit cells and a heating agent are alternately laminated, and which uses Mg (magnesium), Ca (calcium), and Using a mixed molded body of these alloy powders, an oxidizing agent powder selected from nitrates, perchlorates, or chromates, various molten salts typified by lithium chloride-potassium chloride molten salt, and an inorganic binder, The heat insulating layer is configured to actively start generating heat when the battery is in operation.

The present invention will be explained in detail below with reference to representative examples thereof.

FIG. 1 is a sectional view of a stacked thermal battery. 1 in the diagram
is a unit cell, and a representative example was mentioned above. Reference numeral 2 is a heating agent, and a typical example thereof was also described above. Reference numeral 3 denotes an igniter which emits a flame when a pulse current is applied from starting terminals 4a and 4b, and has the role of igniting the heating agent 2 through the fire channel 5. 6 is a heating element for a heat insulation layer of the present invention, which is a central component of the heat insulation layer, and contains magnesium powder of 100 to 42 mesh (0.149 mm) as a metal powder.
~0.35 mm size particles), potassium nitrate (KNO ₃ ) powder as an oxidizing agent, potassium chloride-lithium chloride eutectic salt, and silica powder (SiO ₂ ) as an inorganic binder in a 35:20:30:15 mixture ( % by weight) and rotated in a ball mill mixer for about 1 hour to make it uniform. After mixing, the mixture is taken out, a predetermined amount (approximately 1.2 g is used for a 30 mm battery) is weighed out into a mold, pressure-molded at 1 ton/cm ² , and taken out from the mold. It is very convenient to adjust the calorific value to some extent by adjusting the mixing ratio of the magnesium powder or the mixing ratio of the oxidizing agent KNO ₃ . In this case, if fine powder magnesium of 100 meshes or less is used, the calorific value per unit time is large, but the exothermic reaction ends in a too short time.
It is preferable to use particles of appropriate size as described above. When the exothermic reaction of the heating element 6 is heated by the heating agent 2 placed on both sides of the heating element 6, the molten salt melts and the oxidizing agent KNO ₃ is activated, causing the following reaction of heat of formation with the magnesium powder. Let's do it.

Mg + KNO ₃ → MgO + KNO ₂ + (-ΔH _f゜) (Here, -ΔH _f゜ is the standard enthalpy of formation, which is -601.70ΔH _f゜/Kjmol ^-1 .) This reaction continues while the molten salt is dissolved. continues to diffuse sequentially, and the stacked end unit cell 1' is therefore kept warm.

7 is a heat-resistant heat insulating material provided outside the heating element 6. 8a and 8b are output terminals, 9 is an exterior lid having a glass-sealed terminal, and 10 is an exterior case whose fitting portion with the exterior lid 9 is completely sealed by welding. Reference numeral 11 denotes a heat insulating layer for keeping the laminate warm and preventing thermal damage to the outside of the battery.

FIG. 2 shows a partially enlarged view of the heat insulating layer. In the figure, 1 is a unit cell, and 2 is a heating agent. 21 is 0.1
mm thick iron plate, 22 is magnesium particles, 23 is an oxidizing agent, which is a mixture of the oxidizing agent, molten salt, and an inorganic binder, and is processed into pellets by pressure molding as described above.

The above basic configuration is almost the same as the conventional example, but
Unlike the conventional structure in which the heat of the heating agent is stored in the heat insulating layer for the laminate, this structure is characterized by the provision of a layer that spontaneously generates heat by receiving the heat of the heating agent.

Although the above embodiment does not react in any way during storage of the thermal battery, once the battery is activated, the heating element 6
starts an exothermic reaction and begins to keep the laminate warm.

As mentioned above, the molten salt used for the heating element 6 may be the same as the electrolyte used inside the unit cell, or a molten salt with a lower melting point can also be used, so it can exhibit heat retention ability over a wide temperature range. Therefore, the battery life is also extended.

FIG. 3 shows voltage curves when a conventional example A with a 12-cell series configuration and no heating element 6 and a battery B of the present invention according to an example were discharged at a high rate of 400 mA/cm ³ at -40°C. Conventional example A has almost no difference from B until 20 seconds, but after 20 seconds, the temperature drops severely because the heat dissipation from the unit cells at the end of the stack is large, and for this reason, the electrolyte becomes passive due to solidification. However, in the case of battery B of the present invention, since the heating element 6 generates heat during battery operation as described above, a rapid temperature drop is prevented, and the voltage decreases. The decline will also be slow.

In the above example, an example using magnesium powder was described, but when calcium particles are used, the reaction becomes active, and the standard enthalpy of formation is 635.09ΔH _f
It shows a slightly high value of ゜/KJmol ^-1 . In the alloy example
Mg ₂ Ca (calcium mixing ratio 45% by weight, melting point 714℃)
A similar experimental sample was made and confirmed using particles of , but it generated heat somewhat similar to that of calcium.

In addition to the above-mentioned potassium nitrate, potassium perchlorate (KClO ₄ ) and potassium chromate were confirmed as oxidizing agents, and although they showed similar effects, the exothermic reaction proceeded most smoothly with potassium nitrate. As for the molten salt, we investigated a mixed salt of potassium bromide and lithium bromide (KBr52% by weight, LiBr48% by weight, melting point 330℃), and found that although it was slightly inferior to potassium chloride-lithium chloride, it was not a problem for practical use. .

As described above, according to the present invention, the operating time can be extended by the heat-retaining layer that spontaneously generates heat.
As long-term thermal battery technology takes a step forward,
The effect is tremendous.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a laminated thermal battery used in an example of the present invention, FIG. 2 is a longitudinal sectional view showing an example of the structure of a heat insulating layer, and FIG. 3 is a diagram comparing discharge voltage characteristics. 1...Battery, 2...Heating agent, 6...Heating element,
22... Reducing metal powder, 23... Oxidized layer.

Claims (1)

[Scope of Claims] 1. A heat insulating layer is provided at the end of the main power generation section in which unit cells and heating agents are alternately laminated, and the heat insulating layer contains at least reducing metal powder, oxidizing material powder, and molten salt. 1. A thermal battery comprising: a heating element made of a mixed molded body of powder and an inorganic binder; and configured to start an exothermic reaction when the heating element is heated by a heating agent. 2. The thermal battery according to claim 1, wherein the reducing metal powder is Mg, Ca or an alloy powder thereof, and the oxidizing material powder is a nitrate or chromate. 3. The thermal battery according to claim 2, wherein the molten salt powder is a eutectic salt.