JP2847983B2 - Method for producing positive electrode active material for thermal battery and thermal battery using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a positive electrode active material for a thermal battery and a thermal battery using the same.
The present invention relates to a method for producing a positive electrode active material for a thermal battery in which the positive electrode active material of an iron disulfide-based thermal battery is improved, and a thermal battery using the same.

[0002]

2. Description of the Related Art A thermal battery is inactive at room temperature, but becomes active when heated to a high temperature, and can supply electric power to the outside, and is a kind of storage battery. Therefore, 5
Even after storage for up to 10 years or more, it is used as an emergency power supply because the battery characteristics do not change at all after production. Since this battery is operated at high temperature, the electrode reaction is easy to proceed and there is little polarization, so it has excellent high rate discharge characteristics,
Another feature is that power can be taken out instantly when a start signal is input when use is desired. However, in recent years, higher output has been increasingly demanded, and in particular, high potential is often required. On the other hand, the open circuit voltage of the unit cell in the iron disulfide thermal battery using lithium as a negative electrode is about 2.2 to 2.3 V. The operating voltage at the time of discharge, in the case of a positive electrode reaction as the discharge proceeds, occurs at a deep portion of the positive electrode layer away from the current collector and increases the electric resistance.
It must be designed between 6V and 1.8V. For this reason, when high voltage output is required, the number of unit cells stacked increases, and the volume and weight of the battery increase, making it difficult to reduce the size and weight of the battery.

As a technique conventionally used to solve this problem, a method of adding a highly conductive substance to a positive electrode mixture containing iron disulfide as a positive electrode active material has been studied.
It has been studied to add a stainless powder or a graphite powder as a conductive material into the positive electrode mixture.

[0004]

However, the above two methods are not practical due to the following problems.
That is, in the case of the former, since the stainless steel sheet was also used initially as the positive electrode current collector, the positive electrode active material FeS ₂ was used.
It was expected to be a material that did not easily react with and used. However, as a result, although the electron conductivity in the positive electrode mixture is improved, the reactivity is high due to the use of powdered stainless steel, and iron disulfide and iron in the stainless steel powder are reacted by the following formula: FeS ₂ + Fe ⇒ 2FeS Iron has a fatal drawback that the discharge capacity is rather reduced since the decomposition reaction is easily caused by iron.
Further, in the latter case, there is a problem that the graphite powder is bulky, the positive electrode layer is thickened, the volume of the unit cell is increased, and the battery is increased in size.

The present invention solves such a conventional problem, reduces the rise in internal resistance in the positive electrode layer during discharge, supplies a high operating voltage, and provides a small and lightweight thermal battery. It is an object of the present invention to provide a method for producing a positive electrode active material for use and a thermal battery using the same.

[0006]

Means for Solving the Problems To solve this problem, a method for producing a positive electrode active material for a thermal battery according to the present invention and a thermal battery using the same are characterized in that iron powder or iron oxide or water having at least a surface is used as a starting material. Iron powder, which is iron oxide, a step of mixing the three using metal vanadium powder and sulfur, a step of heating and synthesizing the mixture at a temperature of 350 ° C to 500 ° C, and a step of pulverizing the compound. A method for producing a positive electrode active material through a positive electrode active material, wherein the vanadium content ratio in the obtained positive electrode active material is 5 to 20% by weight. And
The positive electrode active material synthesized as described above is mixed with an electrolyte and a binder to form a positive electrode mixture, and the lithium or lithium alloy of the negative electrode is combined with an electrolyte layer mainly containing a binder powder holding the electrolyte. A unit cell is formed, and a lithium / iron disulfide-based heat cell is formed by combining this with a heating agent.

[0007]

According to this structure, in the positive electrode active material for a thermal battery of the present invention and the thermal battery using the same, vanadium is sulfided at the same time as iron is sulfided, so that vanadium is contained in the crystal lattice of iron disulfide. A complex compound of incorporated iron disulfide and vanadium disulfide is formed. This vanadium disulfide is a semiconductor material, and the electron conductivity in the temperature range where the battery operates is significantly increased. For this reason, the internal resistance in the positive electrode mixture decreases, and as a result, the operating voltage of the unit cell increases.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for producing a positive electrode active material for a thermal battery according to one embodiment of the present invention and a thermal battery using the same will be described with reference to the drawings. In FIG. 1, iron powder or iron powder whose surface is at least iron oxide or iron hydroxide, vanadium powder, and sulfur are used as starting materials. For iron powder and vanadium powder, powder having a particle size of 350 mesh or less is used. Was used. The mixing ratio of the raw materials was set such that the content of vanadium in the cathode active material to be synthesized was a predetermined weight%, and both iron and vanadium were disulfides. For example, when producing a positive electrode active material containing 10% by weight of vanadium, a mixing ratio of 36.6% by weight of iron powder, 10% by weight of metal vanadium, and 53.4% by weight of sulfur is set. . The amount of sulfur at this time is the amount necessary for iron and vanadium to become iron disulfide. In this example, the weight of each mixture was 500 g, and the weighed raw materials were mixed for 1 hour by a porcelain ball mill mixer. Thereafter, the mixture was placed in a porcelain crucible and capped, and further placed in an iron container with a lid, and heat-synthesized at 450 ° C. for 3 hours in an electric furnace. 270 ° C to 690 ° C for heat synthesis
Although it is possible up to 350 ° C., the progress of the sulfurization reaction is slow at a temperature lower than 350 ° C., and at a temperature higher than 500 ° C., the produced iron disulfide starts to decompose. After cooling, the composite was placed in a porcelain mortar and ground to a particle size of 200 mesh or less. Further, in this example, the above-mentioned heating synthesis step and pulverization step were repeated three times, and the final synthesized product was used as the positive electrode active material. Sulfidation can be performed by one heat synthesis, but it is preferable to repeat the heat synthesis step and the pulverization step a plurality of times in order to make higher-quality sulfide, that is, more disulfide.

Although iron powder is used as one of the raw materials in the above embodiment, at least the surface is made of iron hydroxide produced by a method started in Japanese Patent Application Laid-Open No. 58-115031. Even if iron powder is used, a positive electrode active material having the same effect can be obtained, and sulfuration of iron is promoted, so that a high-quality one can be obtained.

FIG. 2A shows a vanadium content of 1 in this embodiment.
FIG. 2B shows an X-ray diffraction pattern of 0% by weight of the positive electrode active material, and FIG. 2B shows an X-ray diffraction pattern of the conventional positive electrode active material. In FIG. 2A, a peak that can be identified as that of VS ₂ indicated by a mark and a diffraction peak of FeS ₂ that are indicated by a mark ● are present, and the crystal structures of both are present alone or in combination. A unit cell having a cross section as shown in FIG. 3 was constructed using the positive electrode active material synthesized according to the present example as described above, and a stacked thermal battery as shown in FIG. 4 was prototyped. The unit cell 4 in FIG. 3 includes a positive electrode active material according to the present embodiment,
Positive electrode layer 1 mainly composed of a mixture of a LiCl-KCl molten salt electrolyte and a SiO ₂ binder for holding the electrolyte
And a negative electrode layer 2 in which lithium as a negative electrode active material is fixed by iron powder, and an electrolyte layer 3 mainly composed of a powder molding layer in which a LiCl—KCl molten salt is held by an MgO binder.
Are formed as an integral molded body. Using the unit cell 4 configured as described above, a laminated thermal battery was prototyped. FIG.
In the figure, reference numeral 4 denotes a unit cell shown in FIG. 3 in which a required voltage can be easily obtained by forming a required number of batteries in series and alternately laminated with a heating agent 5 mainly composed of a uniform mixture of potassium chlorate and iron powder. I do. Reference numeral 8 denotes an igniter whose lead wire is connected to a pair of igniter terminals 9. When a pulse current is supplied from this terminal, a flame is emitted and the heat pad 10 is burned.
It is propagated by burning the squib 11. Reference numerals 12 and 13 denote positive and negative output terminals, which are connected to internal lead wires 14 and 15 taken out from the uppermost portion and the lowermost portion of the stack. Reference numeral 16 denotes a heat insulating material, reference numeral 17 denotes a battery cover, and reference numeral 18 denotes a battery case, both of which are made of stainless steel, and their fitting portions are welded and sealed.

[0011] The positive electrode active material was evaluated using the laminated thermal battery configured as described above. FIG. 5 shows the use of the positive electrode active material when a constant-current discharge of a current density of 500 mA / cm ² was carried out by experimentally producing a laminated thermal battery by changing the vanadium content in the positive electrode active material of the present example. This is the result of calculating the rate. The vanadium content of the positive electrode active material has an effect on the utilization rate, and particularly the vanadium content is 5 to 20% by weight.
In the range, the utilization rate is 45% or more,
It can be said that this is an area of great industrial value in terms of weight reduction. Next, the result of comparing the effect of the present embodiment with the comparative example will be described. FIG. 6 shows a cell having a diameter of 43 mm, a battery outer diameter of 55 mm, and a battery thickness of 3 mm.
FIG. 8 is a diagram showing the results of a constant current discharge test at a current density of 500 mA / cm ² in a shape of 8 mm. In order to check the cell resistance, the open voltage is simultaneously measured at intervals of 20 seconds from the start of discharge, and the resistance per cell is read from the difference between the open voltage and the voltage at the time of load. The result of the reading is shown in FIG. The number of unit cells in series is 15. FIG. 6A shows the discharge curve of the battery of this embodiment, and FIG. 6B shows the discharge curve of the conventional battery. The discharge curve B was such that the operating voltage per cell was low and less than 2.0 V immediately after the operation, and the duration to the final voltage 24 V was short. The discharge curve A has an average operating voltage of 2.1 V per cell, and is higher by about one cell when comparing the voltage level with the discharge curve B. Further, from this, the discharge time is improved to 1.3 times in the present embodiment as compared with the conventional example in the duration up to the final voltage of 24 V. FIG. 7A shows the cell resistance of the battery of this embodiment, and B shows the cell resistance of the conventional battery. From the results shown in FIG. 7, the cell resistance during discharge is about 13% smaller in the present embodiment than in the conventional example. This difference in the cell resistance is attributed to the difference in the positive electrode active material, and is considered to be due to the improvement in the electron conductivity of vanadium disulfide contained in the positive electrode active material of this example. From the above results, the discharge characteristics are improved.

[0012]

According to the present invention, as is apparent from the above description of the examples, according to the method for producing a positive electrode active material for a thermal battery of the present invention and the thermal battery using the same, as the positive electrode active material, A composite compound of iron disulfide and vanadium disulfide with a small increase in internal resistance in the positive electrode layer during discharge can be easily made, and a thermal battery using this can improve the average operating voltage level and improve the utilization rate of the positive electrode active material. Can be improved. Therefore, the effect that a small and lightweight high-performance thermal battery can be provided is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method for producing a positive electrode active material for a thermal battery according to one embodiment of the present invention and a process for producing the positive electrode active material for a thermal battery in a thermal battery using the same.

FIG. 2 is an X-ray diffraction pattern diagram of the positive electrode active material.

FIG. 3 is a cross-sectional view illustrating a configuration of a unit cell.

FIG. 4 is a longitudinal sectional view of a stacked thermal battery configured using the unit cell of FIG. 3;

FIG. 5 is a graph showing the relationship between the vanadium content of the positive electrode active material for a thermal battery and the positive electrode utilization factor.

FIG. 6 is a graph showing the relationship between the discharge voltage, open voltage, and duration of the batteries of this embodiment and the conventional example.

FIG. 7 is a graph showing cell resistance during discharge of FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode layer 2 Negative electrode layer 3 Electrolyte layer 4 Unit cell

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01M ^6/ 30-6/36 H01M 4/58

Claims (3)

(57) [Claims] 1. A step of mixing iron powder or iron powder whose surface is at least iron oxide or iron hydroxide, metal vanadium powder and sulfur as starting materials, and mixing the mixture at 350 ° C. to 500 ° C. A method for producing a positive electrode active material for a thermal battery, comprising a step of heating and synthesizing at a temperature of the following, and a step of subsequently pulverizing the composite, wherein the content of vanadium in the composite is 5 to 20% by weight. 2. The method for producing a positive electrode active material for a thermal battery according to claim 1, wherein the step of heating and synthesizing and the step of pulverizing the compound are repeated a plurality of times. 3. A step of mixing iron powder or iron powder whose surface is at least iron oxide or iron hydroxide, metal vanadium powder and sulfur as starting materials, and mixing the mixture at 350 ° C. to 500 ° C. A thermal battery mainly comprising a step of heating and synthesizing at a temperature and a step of pulverizing the composite, and using a positive electrode active material having a vanadium content ratio of 5 to 20% by weight in the composite.