JP2006236993A - Thermal cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermal cell having excellent high load discharge characteristics by increasing voltage during large current discharge. <P>SOLUTION: The thermal cell has a plurality of unit cells consisting of a positive electrode, a negative electrode, and an electrolyte arranged between the positive electrode and the negative electrode. The electrolyte contains a salt which melts at operating temperature of the thermal cell, and the positive electrode contains a titanium-contained sulfide as an active material. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermal battery, and more particularly to an active material used for a positive electrode of a thermal battery.

  In general, a thermal battery includes a plurality of unit cells including a negative electrode, a positive electrode, and an electrolyte interposed between the two electrodes. A salt that melts at a high temperature is used as the electrolyte. Since this electrolyte does not have ionic conductivity at room temperature, the thermal battery is in an inactive state. When the electrolyte is heated to a high temperature, it becomes molten and becomes a good ionic conductor, so that the thermal battery becomes active and can supply electricity to the outside.

  A thermal battery is a type of storage battery, and the battery reaction does not proceed unless the electrolyte melts. For this reason, even after storing for a period of 5 to 10 years or more, the same battery characteristics as those immediately after manufacture can be exhibited. Further, in the thermal battery, the electrode reaction proceeds at a high temperature. For this reason, the electrode reaction proceeds much faster than other batteries using an aqueous electrolyte solution or an organic electrolyte solution. Therefore, the thermal battery has excellent large current discharge characteristics. Furthermore, the thermal battery has an advantage that power can be taken out in a short time within one second when a start signal is sent to the battery when the battery is used, although it varies depending on the heating means. For this reason, taking advantage of the characteristics, it is suitably used as a power source for various defense devices such as induction devices and an emergency power source.

  In order to improve the above characteristics, various thermal batteries using iron disulfide as a positive electrode active material have been studied. For the purpose of improving the properties of this positive electrode active material, for example, Patent Document 1 proposes to use a composite material of iron disulfide and iridium disulfide (iridium content: 5 to 20% by weight) as the positive electrode active material. ing. Patent Document 2 proposes to use a composite material of iron disulfide and titanium disulfide (titanium content: 5 to 20% by weight) as the positive electrode active material. Patent Document 3 proposes to use a composite material of iron disulfide and vanadium disulfide (vanadium content: 5 to 20% by weight) as the positive electrode active material.

The unit cell voltage in a practical current density region (about 0.5 to ^{2 A} / cm ² ) in a general thermal battery using iron disulfide as the positive electrode active material and lithium metal as the negative electrode active material is , About 1.8-2V. A thermal battery is often used as a power source for a device having a high output and a large load. For this reason, it is necessary to obtain a required voltage by stacking a plurality of unit cells to form a laminate and electrically connecting them in series.

By the way, in recent years, with the miniaturization and high performance of equipment, the thermal battery performance is required to maintain a high voltage in a large current discharge of 1 to ^{2 A} / cm ² or more and to have excellent high load discharge characteristics. Has been. Moreover, it is required to increase the voltage of the unit cells to reduce the number of unit cells to be used and to reduce the height of the stacked body, that is, the height of the thermal cell.
When the thermal battery is discharged at a current density of about 0.5 A / cm ² , the voltage of the unit cell using the above composite material containing iron disulfide as the positive electrode active material is about 2.1 V, and Since the voltage is higher than the voltage (about 1.8 V) of the unit cell using iron sulfide alone, it is possible to reduce the height of the thermal cell.

However, when the thermal battery is discharged with a large current discharge having a current density of 1 to ² A / cm ² , the voltage of the unit cell using iron disulfide alone as the positive electrode active material is about 1.6 to 1.8 V. On the other hand, the voltage of the unit cell using the composite material containing iron disulfide is about 1.7 to 1.9 V, about 1.6 to 1.9 V, and about 1.6 to 1.8 V, respectively. It is. Thus, when discharging with a large current, the voltage of the unit cell using the composite material containing iron disulfide as the positive electrode active material is the same as the voltage of the unit cell using iron disulfide alone as the positive electrode active material. Almost no change, and the effect of high voltage during discharge is reduced.
JP-A-5-242896 Japanese Patent No. 2847982 Japanese Patent No. 28479983

  Accordingly, an object of the present invention is to provide a thermal battery having excellent high-load discharge characteristics by increasing the voltage during large current discharge in order to solve the above-described conventional problems.

The thermal battery of the present invention includes a plurality of unit cells made of a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode, and the electrolyte includes a salt that melts at an operating temperature of the thermal battery, The positive electrode includes a titanium-containing sulfide as an active material.
The titanium-containing sulfide has a general formula: Ti _1-α M _α S _x (where M is Cr, Mn, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ag, Cd, Sn) And at least one selected from the group consisting of W and α and x satisfy the following conditions: 0 ≦ α ≦ 0.95 and 1.5 ≦ x ≦ 2.75) Is preferred.

  According to the present invention, a high voltage can be maintained even during a large current discharge, and a thermal battery having excellent high load discharge characteristics can be obtained. In addition, it is possible to reduce the number of unit cells to be used and to reduce the size of the high load discharge thermal battery without impairing the high load discharge characteristics.

  The thermal battery of the present invention is an electrolyte containing a positive electrode, a negative electrode, and a salt (molten salt) that is disposed between the positive electrode and the negative electrode and melts at the operating temperature of the thermal battery (in other words, inactive at room temperature). A plurality of unit cells made of an electrolyte that becomes active when melted at a predetermined temperature), and the positive electrode includes titanium-containing sulfide as an active material.

By using a titanium-containing sulfide as the positive electrode active material, the reactivity of the positive electrode is improved. Further, the titanium-containing sulfide that is the positive electrode active material of the thermal battery of the present invention has a higher equilibrium potential of the positive electrode and the overvoltage at the time of discharge is smaller than iron disulfide that is the positive electrode active material of the conventional thermal battery For this reason, the discharge potential of the positive electrode is increased. Therefore, the discharge voltage of the unit cell, that is, the thermal battery increases.
For this reason, a high voltage can be maintained even during a large current discharge, and excellent high load discharge characteristics can be obtained. In addition, it is possible to reduce the number of unit cells to be used and to reduce the size of the high load discharge thermal battery without impairing the high load discharge characteristics.

The titanium-containing sulfide is, for example, a compound represented by the general formula: Ti _1-α M _α S _x . M is at least one element selected from the group consisting of Cr, Mn, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ag, Cd, Sn, and W, and α and x are It is preferable that 0 ≦ α ≦ 0.95 and 1.5 ≦ x ≦ 2.75 respectively.
α represents the substitution amount of the element M, and x represents a deviation from the stoichiometric composition. By replacing a part of titanium with the element M in the range where α is 0.95 or less, the discharge voltage is further increased. When x <1.5 and 2.75 <x, the discharge voltage slightly decreases.

Since the flatness of the discharge voltage can be maintained by improving the crystallinity or the like, x is more preferably 1.75 to 2.25. Since the flatness of the discharge voltage can be maintained by improving the crystallinity, α is more preferably 0.25 to 0.75.
In particular, the element M is more preferably Co in that a high discharge voltage can be obtained. This is presumably because Co easily diffuses uniformly into the solid phase of Ti, improves the homogeneity of the crystal, and easily exhibits the effect of substitution of the element M.
The titanium-containing sulfide is obtained, for example, by mixing titanium powder, sulfur powder, and element M powder with a ball mill or the like, and firing the mixture.

Here, an embodiment of the thermal battery of the present invention will be described with reference to FIG.
A power generation unit in which a plurality of unit cells 7 and heating agents 5 are alternately stacked is housed in a metal outer case 1. An ignition pad 4 is disposed at the top of the power generation unit, and a spark plug 3 is installed in the vicinity of the top of the ignition pad 4. A heat conduction zone 6 is arranged around the power generation unit. Since the heat generating agent 5 includes iron or the like and has conductivity, the unit cells 7 are electrically connected in series via the heat generating agent 5. The exothermic agent 5 is made of, for example, a mixture of Fe and KClO ₄ , and the Fe powder is sintered as the exothermic agent 5 is burned when the battery is activated. The conductivity of the exothermic agent 5 is maintained.

  The outer case 1 is sealed by a battery lid 11 having a pair of ignition terminals 2 and a positive terminal 10a and a negative terminal 10b. The positive electrode terminal 10a is connected to the positive electrode of the unit cell 7 at the top of the power generation unit via a positive electrode lead plate. On the other hand, the negative electrode terminal 10 b is connected to the negative electrode of the unit cell 7 at the bottom of the power generation unit via the negative electrode lead plate 8. A heat insulating material 9a is disposed between the battery lid 11 and the ignition pad 4, and a heat insulating material 9b is filled between the outer case 1 and the power generation unit.

As shown in FIG. 2, the unit cell 7 includes a negative electrode 12, a positive electrode 13, and an electrolyte 14 disposed between the negative electrode 12 and the positive electrode 13.
The positive electrode 13 is made of, for example, a mixture of the above titanium-containing sulfide powder, a binder such as silica powder, and a salt used for the electrolyte 14 described later. This salt is used to improve ionic conductivity.

  The negative electrode 12 includes a negative electrode mixture layer 15 containing a negative electrode active material, and an iron cup-shaped current collector 16 that houses the negative electrode mixture layer 15. The negative electrode mixture layer 15 is made of, for example, a mixture of a negative electrode active material and a conductive material. As the negative electrode active material, for example, a compound containing lithium such as Li metal, Li—Al, or Li—Si alloy is used. As the conductive material, for example, metal powder such as iron, copper, nickel, or manganese, or a carbon material is used. Moreover, in order to improve ion conductivity, the negative mix layer 15 may contain the salt used for the electrolyte 14 mentioned later.

The electrolyte 14 is made of, for example, a mixture of a salt that melts at a high temperature, that is, an operating temperature of a thermal battery, and a holding material such as MgO. Any salt that can be used in a thermal battery, such as an alkali metal salt, a mixture thereof, or a eutectic salt may be used. For example, an alkali metal salt such as LiCl, KCl, or AlCl ₃ , or a eutectic salt such as LiCl—KCl, LiCl—LiBr—LiF, LiCl—LiBr—KBr, or LiNO ₃ —KNO ₃ is used.

The operation of the thermal battery will be described below.
When a high voltage is applied to the ignition terminal 2 from a power source connected to the ignition terminal 2, the spark plug 3 is ignited. Thereby, combustion is transmitted to the ignition pad 4 and the igniting zone 6, the heat generating agent 5 burns, and the unit cell 7 is heated. Then, the electrolyte 14 of the unit cell 7 is melted to become a molten salt, that is, an ionic conductor. In this way, the battery is activated and can be discharged.

In the above description, an internal heating type thermal battery in which an ignition plug is provided inside the battery and the power generation unit is heated from inside the battery to activate the battery has been described. However, the present invention does not include an ignition plug inside the battery. Also, the present invention can be applied to an external heating type thermal battery in which the power generation unit is heated from the outside of the battery by a burner or the like to activate the battery.
Examples of the present invention will be described in detail below, but the present invention is not limited to these examples.

Example 1
A unit cell similar to that shown in FIG. 2 was produced by the following procedure. The unit cells were all manufactured in a dry air having a dew point of −45 ° C. or less in an environment in which the influence of moisture was eliminated as much as possible.
(1) Production of positive electrode active material Titanium powder and sulfur powder were mixed in a ratio of 1: 2 by a magnetic ball mill. The obtained mixture was baked by heating at about 450 ° C. for 3 hours in a magnetic crucible to obtain a fired product of TiS ₂ . This fired product was pulverized and classified with a magnetic ball mill to 200 mesh or less to obtain TiS ₂ powder as a positive electrode active material.

(2) Production of positive electrode The TiS ₂ powder obtained above, LiCl-KCl as eutectic salt, and silica powder as a binder at a weight ratio of 240: 110: 7 in a magnetic ball mill. Mixed. This mixture was baked at 450 ° C. for 1 hour under an argon gas atmosphere. Thereafter, the fired product was pulverized and classified to 200 mesh or less with a magnetic ball mill to obtain a positive electrode mixture. This positive electrode mixture was pressure-molded into a disk shape having a diameter of 13 mm and a thickness of 0.4 mm at a pressure of ² ton / cm ² to obtain a positive electrode 13.

(3) and LiCl-KCl as producing eutectic salt of the cell, and MgO were mixed in a weight ratio of 60:40 as the holding material, the resulting mixture 2 ton / cm ² in diameter 13mm and thickness at a pressure of 0. The electrolyte 14 was obtained by pressure forming into a 4 mm disk shape.

The negative electrode 12 was produced as follows.
A negative electrode mixture layer 15 made of a disc-shaped Li foil having a diameter of 11 mm and a thickness of 0.7 mm is placed in a cup-shaped current collector 16 made of stainless steel SUS304, and the opening end of the current collector 16 is bent inward. Then, the peripheral edge portion of the negative electrode mixture layer 15 was caulked and clamped between the bent portion and the bottom portion of the current collector 16. In this way, the negative electrode mixture layer 15 was fixed in the current collector 16 to obtain a disc-shaped negative electrode 12 having a diameter of 13 mm and a thickness of 1.2 mm.
The positive electrode 13 and the negative electrode 12 obtained above were overlapped via an electrolyte 14 to obtain a unit cell.

<< Examples 2 to 7 >>
Titanium powder and sulfur powder were mixed at an atomic ratio of 1: x in a magnetic ball mill. The obtained mixture was baked by heating at about 450 ° C. for 3 hours in a magnetic crucible to obtain a fired product of TiS _x . This fired product was pulverized and classified with a magnetic ball mill to 200 mesh or less to obtain TiS _x powder as a positive electrode active material.
At this time, positive electrode active materials were prepared by changing the x value of TiS _x as shown in Table 1 in various ways. Then, using these positive electrode active materials, unit cells were produced in the same manner as in Example 1.

<< Examples 8 to 69 >>
Titanium powder, element M powder, and sulfur powder were mixed in a magnetic ball mill at an atomic ratio of 1-α: α: x. This mixture was heated in a magnetic crucible at about 450 ° C. for 3 hours and fired to obtain a fired product of Ti _1-α M _α S _x . This fired product was pulverized and classified with a magnetic ball mill to 200 mesh or less to obtain Ti _1-α M _{α Sx} powder as a positive electrode active material.
At this time, positive electrode active materials were prepared by changing the α value, x value, and element M of Ti _1-α M _α S _x in various ways as shown in Tables 2 to 5. Then, using these positive electrode active materials, unit cells were produced in the same manner as in Example 1.

<< Comparative Example 1 >>
Iron powder and sulfur powder were mixed at a ratio of atomic ratio of 1: 2 by a magnetic ball mill. This mixture was baked by heating at about 450 ° C. for 3 hours in a magnetic crucible to obtain a fired product of FeS ₂ . The fired product was pulverized and classified with a magnetic ball mill to 200 mesh or less to obtain FeS ₂ powder as a positive electrode active material. Using this positive electrode active material, a unit cell was produced in the same manner as in Example 1.

<< Comparative Example 2 >>
Sulfur powder, iron powder, and iridium powder were mixed at a weight ratio of 53.4: 36.6: 10. The mixture was baked by heating at about 450 ° C. for 3 hours in a magnetic crucible. The fired product was pulverized in a magnetic mortar and pulverized and classified to 200 mesh or less. This firing step and pulverization step were alternately repeated three times to obtain a composite material (iridium content: 10% by weight) of FeS ₂ and IrS ₂ as a positive electrode active material. Using this positive electrode active material, a unit cell was produced in the same manner as in Example 1.

<< Comparative Example 3 >>
A composite material of FeS ₂ and TiS ₂ (titanium content: 10% by weight) was obtained as a positive electrode active material by the same method as in Comparative Example 2 except that titanium powder was used instead of iridium powder. Using this positive electrode active material, a unit cell was produced in the same manner as in Example 1.

<< Comparative Example 4 >>
A composite material of FeS ₂ and VS ₂ (vanadium content: 10% by weight) was obtained as a positive electrode active material by the same method as in Comparative Example 2 except that vanadium powder was used instead of iridium powder. Using this positive electrode active material, a unit cell was prepared in the same manner as in Example 1.

[Evaluation]
The following evaluation was performed about the unit cell produced above.
A test cell was constructed by sandwiching a unit cell between two hot plates capable of controlling the temperature. Then, the test cell was subjected to constant current discharge (end voltage: 0.4 V), and the discharge voltage of the unit cell was examined.
The discharge test was performed by heating the unit cell to 550 ° C., which is an average operating temperature of a thermal cell using LiCl—KCl as an electrolyte, with a hot plate. The voltage at the time when 10 seconds had elapsed from the start of discharge was taken as the discharge voltage. The current density was 0.5, 1.0, 1.5, and 2.0 A / cm ² .
The results of the discharge test are shown in Tables 1-6.

In the unit cells of Examples 1 to 7 using TiS _x as the positive electrode active material, the voltage at the time of discharging with a current density of 0.5 to ² A / cm ² exceeded 2 V, and the unit cells of Comparative Examples 1 to 4 Compared with the discharge voltage increased.
This is because the positive electrode active materials of Examples 1 to 7, which are titanium-containing sulfides, have higher reactivity than the positive electrode active materials of Comparative Examples 1 to 4 containing iron disulfide, and have a high equilibrium potential. This is considered to be because the overvoltage of is small.
In the unit cells of Examples 2 and 7 in which Ti <x> x <1.5 or 2.75 <x in TiS _x , the discharge voltage was slightly lowered because the positive electrode active material was not a single phase. From this, it was found that x is preferably 1.5 to 2.75.

In Ti _1-α M _α S _x , α is 0 to 0.95, x is 1.5 to 2.75, and element M is Cr, Mn, Co, Ni, Cu, Zn, Ge, Zr, Nb, In the unit cell using the positive electrode active material of Mo, Ag, Cd, Sn, or W, the voltage at the time of discharge with a current density of 0.5 to ² A / cm ² exceeded 2 V, and the discharge voltage was greatly increased. .
Among these, the unit cells of Examples 16 to 25, in which the element M is Co, had a large discharge voltage and exhibited excellent high load discharge characteristics. This is presumably because Co is easily diffused uniformly in the solid phase of Ti, the crystal homogeneity is improved, and the effect of substitution of the element M is easily exhibited.

In the unit cell using a positive electrode active material having an α of 0.98 in Ti _1-α M _α S _x , compared with Comparative Examples 1 to 4 when discharging at a current density of 0.5 and 1.0 A / cm ^2. Even a large voltage was obtained.
However, in a unit cell using a positive electrode active material having an α of 0.98, a positive electrode active material having an α of 0.95 is used particularly during a large current discharge with a current density of 1.5 to 2.0 / cm ^2. The discharge voltage was lower than that of the unit cell used. This is because if the substitution amount α of the element M exceeds 0.95, the effect of the substitution of the element M such as an increase of the discharge voltage becomes too large, and the effect of improving the reactivity by Ti becomes relatively smaller than that. It is thought that it was because of. From this, it was found that the substitution amount α of the element M is preferably 0.95 or less.

<< Examples 70 to 74 >>
A positive electrode active material was obtained in the same manner as in Example 2 _except that the elements M, α, and x in Ti _1-α M _α S _x were changed as shown in Table 7. At this time, as shown in Table 7, two kinds of elements M (atomic ratio 1: 1) were used in combination. For example, the composition of the positive electrode active material of Example 70 using Co and Cr as the element M is Ti _0.5 Co _0.25 Cr _0.25 S ₂ .
Using these positive electrode active materials, a unit cell was produced in the same manner as in Example 1, and a discharge test similar to the above was performed. The results are shown in Table 7.

From Table 7, even when two kinds of elements M are used in combination, a voltage higher than that of the unit cells of Comparative Examples 1 to 4 can be obtained under any discharge condition, and a current density of 0.5 to ^{2 A} / cm ^2. The voltage at the time of discharging was over 2V, and the discharging voltage was greatly increased.
In addition to the combination of the element M shown in this embodiment, two or more elements of Cr, Mn, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ag, Cd, Sn, and W are combined. Even in this case, the same effect as the present embodiment can be obtained.

<< Examples 75 to 91 >>
A thermal battery having the same structure as that shown in FIG. 1 was prepared. The thermal batteries were all manufactured in a dry air having a dew point of −45 ° C. or less in an environment in which the influence of moisture was eliminated as much as possible.
The power generation unit is configured by alternately stacking the unit cells 7 and the heat generating agent 5. At this time, 13 unit cells 7 were used. As the exothermic agent 5, a mixture of Fe and KClO ₄ was used, and the mixing ratio was adjusted so that the average temperature during battery operation was 550 ° C.

The ignition pad 4 was arranged on the upper part of the power generation unit, and the surrounding area was covered with a igniting zone 6. A mixture of Zr, BaCrO ₄ , and glass fiber was used for the ignition pad 4 and the igniting zone 6.
As an igniter for the spark plug 3, a mixture of potassium nitrate, sulfur, and carbon at a weight ratio of 75:10:15 was used. As the heat insulating materials 9a and 9b, ceramic fiber materials mainly composed of silica and alumina were used. In this way, a thermal battery having an operating temperature of 550 ° C. was produced.

At the time of producing the thermal battery, the unit cells (Ti, _{In 1-α} M _α S _x , α is 0 or 0.5, x is 2, and M is Cr, Mn, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ag, Cd, Sn Or W.) was used to manufacture thermal batteries of Examples 75 to 91, respectively.

The following discharge test was done about the thermal battery obtained above. A high voltage was applied from the power source connected to the ignition terminal, the ignition plug was ignited, and the thermal battery was activated. The thermal battery was discharged at a current density of 0.5 A / cm ² (end voltage: 7.8 V) or 2 A / cm ² (end voltage: 6.5 V), and the voltage at the time when 10 seconds had elapsed from the start of discharge ( The discharge voltage) was examined. As a result, it was found that a high discharge voltage corresponding to 13 unit cells was obtained.
In the above example, the content of LiCl—KCl in the positive electrode was about 31% by weight and the content of silica powder was about 2% by weight. However, these contents are not particularly limited, and the strength and performance of the positive electrode are affected. The necessary amount may be added as appropriate.

  The thermal battery of the present invention is suitably used as a power source for various defense devices such as induction devices and an emergency power source.

It is the perspective view which made a part of the thermal battery which concerns on one embodiment of this invention notched, and was made into the cross section. It is a disassembled sectional view of the unit cell used for the thermal battery of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exterior case 2 Ignition terminal 3 Spark plug 4 Ignition pad 5 Heating agent 6 Heating zone 7 Unit cell 8 Negative electrode lead plate 9a, 9b Thermal insulation material 10a Positive electrode terminal 10b Negative electrode terminal 11 Battery cover 12 Negative electrode 13 Positive electrode 14 Electrolyte 15 Negative electrode mixture Layer 16 Current collector

Claims (2)

A thermal battery comprising a plurality of unit cells made of a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode,
The electrolyte includes a salt that melts at an operating temperature of the thermal battery, and the positive electrode includes a titanium-containing sulfide as an active material. The titanium-containing sulfide has a general formula: Ti _1-α M _α S _x (where M is Cr, Mn, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Ag, Cd, Sn) And at least one selected from the group consisting of W and α and x satisfy the following conditions: 0 ≦ α ≦ 0.95 and 1.5 ≦ x ≦ 2.75) Item 2. The thermal battery according to item 1.

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