JPH0740488B2 - Method for producing positive electrode mixture for thermal battery and thermal battery using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to suppressing the spike voltage of a lithium / iron disulfide-based thermal battery and flattening the discharge voltage.

2. Description of the Related Art A thermal battery is a type of storage battery that is inactive at room temperature, but can be activated by heating to a high temperature to supply electric power to the outside. Therefore, it can be used even after storage for 10 years or more without changing the battery characteristics immediately after production, and thus it is used for various emergency power sources.
In addition, since it is operated at high temperature, the electrode reaction is easy to proceed, so it is excellent in large current discharge characteristics, and when it is desired to use it, it has features such that power can be taken out instantly by inputting a start signal with a simple operation. . On the other hand, there is a tendency that the voltage range on the side of the equipment used becomes severer, and it is desired that the operating voltage be as flat as possible.

In the thermal battery, this specific phenomenon is a primary high voltage that appears in the initial state where the voltage starts to rise when a starting signal is input to the thermal battery, the heat generating agent is burned, and the unit cell is heated. Generally referred to as spike voltage. That is, it refers to a momentary peak voltage that occurs in about 0.5 to 2 seconds after applying a start signal, and a phenomenon that a voltage pattern becomes a stable voltage immediately after that. When a device is designed using a battery having such a voltage characteristic, a high voltage component must be used in consideration of safety in an electric circuit, and the device becomes large and heavy.

The cause of the spike voltage is iron disulfide (Fe
It is thought that this is due to the oxide and sulfate coatings formed on the powder surface of S ₂ ). This is iron sulfate (Fe
SO ₄₎ or by heating the reaction in a sealed tube to produce the FeS ₂ with poly alkali sulfide, and the iron (Fe) powder when producing FeS ₂ is reacted with alkali sulfite, iron oxide on the surface of the FeS ₂ , Because iron sulfate is formed or remains. These compounds with respect to FeS ₂ becomes stable voltage of FeS ₂ When the potential is high, the surface coating by the discharge is broken.

FeS ₂ with surface coating layer and single crystal FeS ₂ without surface coating layer
It is proved that in the former case, spike voltage is generated in the former, but FeS ₂ in the latter is not observed. Therefore, the following three points have been studied conventionally.

(1) Flowing hydrogen sulfide gas (H ₂ S) through untreated FeS ₂ 3
Heat reaction at 50 ° C to convert surface impurities into FeS ₂ .

(2) Li _x FeS ₂ prepared by heating reaction of FeS (iron sulfide) and Li ₂ S (lithium sulfide) is used.

(3) Calcium disilicide (CaSi ₂ ) powder is added as a deoxidizing agent.

Problem to be Solved by the Invention The above (1) is the prior art shown in SAND79-0090,1979, in which H ₂ S gas is flowed (floating) at 350 ° C. for 30 hours.
By firing in an electric furnace for 1 minute, the FeS ₂ surface Fe ₂ O ₃ and F
It converts eSO ₄ into pure FeS ₂ and eliminates the voltage rise factor, but requires an aftertreatment device of toxic H ₂ S gas to be released. (2) is International Power So
urces Symposium (IPSS), P677, published in 1986.Since Li ₂ S is extremely sensitive to humidity, it decomposes into LiOH and H ₂ S during handling. Easy,
It gives off a bad smell and has a bad effect on health.

In (3), the CaSi ₂ powder described in the same IPSS, 1982 is used as Fe.
The relative S ₂ powder mixture was added 3-5% by weight, the molten salt electrolyte powder, after a uniform positive electrode mixture powder was added a molten salt -2 silicon oxide powder, which had been used in the battery through the vacuum drying However, there was a problem that the addition of CaSi ₂ causes the capacity to decrease and the voltage waveform to change two steps.

In order to solve the conventional problems as described above, the present invention focuses on the method of adding CaSi _{2 in} (3) above, has no decrease in positive electrode capacity, has an excellent voltage waveform, and suppresses spike voltage as much as possible. It is an object of the present invention to realize a lithium / iron disulfide-based thermal battery and also provide an easy method for treating a positive electrode mixture.

Means for Solving the Problem In order to solve the problem, the present invention provides untreated iron disulfide, molten salt electrolyte, and calcium disilicide in powder form, respectively.
If necessary, an inorganic binder containing an electrolyte is further added to the mixture and mixed and stirred, and a step of heat-treating the mixture in a high-temperature furnace in which argon, nitrogen or a mixed gas thereof is passed, And a step of pulverizing the treated positive electrode mixture in a dry atmosphere to obtain a positive electrode mixture powder.

As the battery, lithium or a lithium alloy was used for the negative electrode, a magnesium oxide (MgO) powder molded body holding a molten salt electrolyte in the electrolyte layer was used, and the positive electrode mixture of the present invention was powdered in the positive electrode layer. By combining a unit cell consisting of three layers as a molding layer and an exothermic agent utilizing the thermite reaction, Li
/ FeS ₂ system thermal battery.

By using this manufacturing method and the above-mentioned thermal battery, the spike voltage as in the conventional case is suppressed to a low level and the operating voltage is flattened. That is, impurities such as iron oxides and iron sulfates formed on the surface of FeS ₂ react with CaSi ₂ during the heat treatment to remove the coating film, so that the FeS ₂ surface becomes active. CaSi
The addition amount of ₂ should be limited as much as possible so that the effect can be obtained, and consideration should be given so that it does not adversely affect other than the spike voltage. If the amount added exceeds 1.5% by weight relative to FeS _{2 and} is 2.0% by weight or more, a two-step wave discharge curve remarkably occurs, and the discharge life is also shortened. Good.

When argon or nitrogen is floated and the positive electrode mixture is heat-treated in a high-temperature firing furnace, impurities in the FeS ₂ surface under the inert atmosphere are easily affected by the molten salt and accelerate the reaction with CaSi ₂ , so the addition amount is small. Can increase the processing effect. Therefore, only the initial spike voltage can be removed without being affected by the discharge life.

In addition, as compared with the case where the positive electrode layer of the unit cell is formed by using the positive electrode mixture in which FeS ₂ powder, the electrolyte powder, and the CaSi ₂ powder are simply mechanically mixed as in the conventional case, When it is used as a layer, the molding density is increased, and the energy density (Wh / l) of the battery can be improved by making the unit battery thinner.

As described above, a thermal battery that is easy to manufacture, has a flat discharge curve with suppressed spike voltage, does not affect the discharge life, and has improved energy density can be configured.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1, 2, and 3.

FIG. 1 shows a manufacturing process drawing of the positive electrode mixture. In the figure, Fe
69% by weight of S ₂ powder (same below), lithium chloride-potassium chloride (LiCl-KCl, melting point 352 ° C) molten salt electrolyte (indicated by E) powder 10%, LiCl-KCl molten salt electrolyte of silicon dioxide (SiO ₂ ) Powder held in binder (displayed as EB) 20
%, 0.5% of CaSi ₂ 100 mesh pass powder are weighed to make the total amount 1 kg. Next, it is put in a ball mill container, sealed, and rotated for 1 hour to obtain a uniform mixed powder. This is transferred to a Pyrex glass container and placed in a floating electric furnace in which an inert gas flows, and argon (Ar) gas is continuously flowed at a gas flow rate of 5 to 50 l / min per 1 kg of the mixture, and the electric furnace is raised. Warm and hold for 1 hour at 370-500 ° C above the melting point of the electrolyte. After this, cool while continuing to flow Ar gas,
Pull the container out at 100 ° C or below and transfer to a dry atmosphere. In this state, it is in a lump shape that is relatively easy to crumble, and it is crushed in a mortar or the like and sized to 50 to 250 mesh to obtain a positive electrode mixture.
Although EB was used here, it may be removed by slightly increasing the E ratio, and nitrogen gas (N ₂ ) or Ar may be used instead of Ar gas.
Mixed gas of N ₂ may be flowed.

Floating gas amount, if less than 5l / min to the charged amount 1Kg if there is fear of mixing of air into the furnace, FeS ₂
However, there is a risk of producing iron oxides, while 50 l / min or more is economically disadvantageous.

The temperature of the high-temperature furnace is preferably 370 ° C lower limit and 500 ° C upper limit in terms of characteristics when LiCl-KCl molten salt is used for the electrolyte.
At temperatures below ℃, the effect of CaSi ₂ is small due to variations in temperature adjustment, and at temperatures above 500 ℃, FeS ₂ gradually decomposes, resulting in poor discharge characteristics.

FIG. 2 shows a sectional view of a unit cell using the positive electrode mixture layer shown in FIG. 1 of the present invention.

Reference numeral 1 is a positive electrode mixture layer, an appropriate amount of which is determined according to the relationship between the amount of discharge electricity and the utilization rate, a specified amount is weighed and placed in a mold, and after low-pressure preforming, it is impregnated with 50% LiCl-KCl. Quantitatively weigh and stack electrolyte powder consisting of MgO binder,
While performing main molding at high pressure to form the electrolyte layer 2,
A two-layer integral pellet is obtained. Reference numeral 3 is a negative electrode cup, 4 is an integrated mixed layer of pure lithium and iron powder arranged on the inner surface of the negative electrode cup 3, or a negative electrode active material layer made of a lithium-aluminum alloy and E. And the unit cell.

FIG. 3 is a vertical cross-sectional view of a laminated type thermal battery using the positive electrode mixture prepared by the manufacturing method of FIG. 1 and the unit cell of FIG.

6 is the unit cell shown in FIG.
The desired voltage can be easily obtained with, and potassium perchlorate and iron powder
And the exothermic agent 7 composed of a uniform mixture of 8,
9 is a heat storage agent layer arranged on the top and bottom of the laminate,
For example, mixed salt of lithium sulfate and sodium chloride and SiO₂Ba
A layer of inder generates latent heat of solidification at 495 ° C
Keeping the pond stack temperature for a long time is not suitable for extending the battery life.
It is an essential heat storage material. 10 is an igniter and its lead wire is a pair
It is connected to the starting terminal 11 of the
When energized, it emits a flame and burns the heat pad 12,
The flame propagates to the blaze zone 13. 14 and 15 are positive and negative
Internal terminals taken from the top and bottom of the stack with force terminals.
Connect to the lead wires 16 and 17. 18 is a heat insulating layer MIN-K Called
Enclose the stack with high performance inorganic insulation
It was 19 is a battery lid and 20 is a battery case, both of which are made of stainless steel.
It is made of steel and the fittings are welded and sealed.

The laminated battery using the present invention burns the igniter 10, the heat pad 12, the squib 13 and the exothermic agent 7 in this order by applying a pulse current from the pair of starting terminals 11 to form the unit cell 6 Start by heating. The unit cell heats up to about 500 ℃, and LiCl-KCl
When the electrolyte is melted, the positive electrode material mixture layer of the present invention starts discharging and supplies a flat output voltage with suppressed spike voltage.

Next, the results of examining the effect of this embodiment will be described. Figure 4 shows
The discharge test results of 100 mA / cm ² current density in a cell shape with a cell diameter of 75 mm, a cell outer diameter of 95 mm, and a cell height of 90 mm are shown. The number of series cells is 15, and the average operating voltage is 2V / cell.

In the figure, A shows the discharge curve of the example of the present invention, and the addition ratio of CaSi ₂ is 0.5%. B shows Conventional Example 1, which is a battery using a positive electrode mixture made without powdery CaSi ₂ and only by powder mixing without a heat treatment step. C indicates Conventional Example 2, CaSi ₂ 5%
It is a battery using a positive electrode mixture made only by powder mixing without addition and heat treatment steps. Battery B showed a spike voltage of 35V immediately after its operation and then dropped sharply to maintain a stable voltage of about 30V, and the duration of 25V or more was 15 minutes or more. Battery C
Although the spike voltage was suppressed to 32V, the result was that the voltage double-stepped wave, the voltage slope increased, and the duration decreased. In the invention sample A, the spike voltage was not completely removed, but was improved to a practically problem-free value of 31.5 V, and there was no effect on the voltage two-stage wave and the duration.
The effect is that the flatness of the voltage is improved.

FIG. 5 was carried out for the purpose of investigating the effect of the CaSi ₂ addition ratio on the spike voltage and the stack height by changing the composition of FeS ₂ , CaSi ₂ , E and EB using the method of the present invention. In Conventional Example 1, since the packing density of the positive electrode mixture was slightly low and the layer thickness was large, the stack height consisting of 15 unit cells and 16 exothermic agents was 47 mm. Sample Nos. 1 to 7 have an effect that the positive electrode mixture and particles are hardened by heat treatment and the packing density is increased, and the positive electrode mixture layer can be formed thinner than in Conventional Example 1, so that the stack height is It became about 1.7 mm lower. Also,
Spike voltage is the same composition as in Conventional Example 1
On the contrary, No.1 increased, but Sample Nos. 2 to 12 added in the range of 0.1 to 5% showed a decreasing tendency, especially 0.3 to 1.5%.
Sample Nos. 3 to 7 in the range of 3) were practical because both effects of spike voltage and stack height were obtained. Sample Nos. 8 to 12 have a practical range in which CaSi ₂ that does not directly participate in the discharge reaction has a bad effect as battery resistance, lowers the operating voltage than the effect of addition, and increases the stack height due to an increase in the unit cell thickness. It wasn't.

In this embodiment, an example in which FeS ₂ , CaSi ₂ , E and EB are mixed at the same time has been described, but similar effects can be obtained even when the following steps are performed.

a) FeS ₂ and CaSi ₂ are mixed in a desired composition, fired in an Ar gas floating electric furnace, cooled, taken out, remixed by adding E and EB, and fired again in an Ar gas floating electric furnace. , How to cool and crush.

b) FeS ₂ , CaSi ₂ and E are used as the three types, and mixing, firing, cooling and pulverization are carried out to increase the amount of EB-deleted part of the electrolyte to E.

EFFECTS OF THE INVENTION As is clear from the above description, not only is calcium disilicide mixed into the positive electrode mixture in powder form, but after mixing with powder, Ar gas, nitrogen gas or a mixed gas thereof is passed. After heat treatment in the high temperature furnace, cooled in the same furnace,
After that, the positive electrode material mixture powder that has been pulverized in a dry atmosphere is used by molding it into a positive electrode material mixture layer of a unit cell, and is combined with a heat generating agent. The spiked high voltage is suppressed and the operating voltage is flattened. Further, the positive electrode mixture that has undergone the same treatment step in the range of 0.3 to 1.5% by weight of CaSi ₂ has the same discharge duration,
Since the molding density is high, the stack height is low and the battery can be miniaturized. In addition, the effect that the manufacturing process is simple and no inconvenience occurs during mass production can be obtained.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of a positive electrode mixture showing an embodiment of the present invention,
FIG. 2 is a sectional view of a unit cell formed by molding the same mixture as a positive electrode mixture layer, and FIG. 3 is a sectional view of a laminated thermal battery of the present invention in which the unit cells of FIG. FIG. 5 is a comparison diagram of the discharge curves of the example of the present invention and the conventional example, and FIG. 5 is a characteristic tendency diagram of the mixture composition, spike voltage, and stack height. 1 ... Positive electrode mixture layer, 2 ... Electrolyte layer, 5 ... Negative electrode, 6 ...
… Battery cell, 7… Exothermic agent.

Claims (5)

[Claims] 1. A negative electrode using lithium or a lithium alloy,
In a thermal battery having an electrolyte layer using a molten salt and a positive electrode using iron disulfide, a step of homogeneously mixing and stirring at least a positive electrode mixture containing iron disulfide, a molten salt and calcium disilicide, and argon and nitrogen. Alternatively, a method for producing a positive electrode mixture for a thermal battery, which comprises a step of performing heat treatment in a high-temperature furnace in which a mixed gas of these is circulated, a step of cooling in the same furnace, and a step of pulverizing in a dry atmosphere. . 2. The production of a positive electrode mixture for a thermal battery according to claim 1, wherein the amount of calcium disilicide added is in the range of 0.30% by weight or more and 1.50% by weight or less with respect to iron disulfide. Law. 3. The amount of flowing gas is a flow rate of 5 to 50 l / min with respect to the charged amount of the positive electrode mixture of 1 kg.
Item 6. A method for producing a positive electrode mixture for a thermal battery according to item. 4. The method for producing a positive electrode mixture for a thermal battery according to claim 1, wherein the heat treatment temperature is in the range of 370 to 500 ° C. 5. A thermal battery in which a positive electrode mixture powder for a thermal battery according to claim 1 is weighed in a fixed amount and pressure-molded in a mold to use a positive electrode mixture layer as a positive electrode.