JP2008141160A - Thermally initiated molten salt capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermally initiated molten salt capacitor which can be applied to a huge electric power storage for short period to long period and can take out electric energy accumulated in a capacitor when it is needed. <P>SOLUTION: The thermally initiated molten salt capacitor comprises a pair of polarizable electrodes and an electrolyte interface made of molten salt, featured by solidifying the molten salt with electric energy accumulated in the capacitor. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a thermally activated molten salt capacitor formed by a pair of polarizable electrodes and an electrolyte interface composed of a molten salt, and in particular, by solidifying the molten salt in a state where electric energy is accumulated in the capacitor, The present invention relates to a capacitor that can re-melt the molten salt and take out the stored electric energy when necessary.

The electric double layer capacitor is a capacitor that uses electric energy accumulated in an electric double layer formed at an interface between a polarizable electrode such as activated carbon and an electrolytic solution. Compared with secondary batteries such as lead-acid batteries, nickel-metal hydride batteries, and lithium batteries, it has stable characteristics at high output and can be deteriorated even after repeated use because it can charge and discharge a relatively large electric capacity instantly. Has very few features.

The electric double layer capacitor is composed of a polarizable electrode having a large surface area, an electrolyte that contacts the polarizable electrode, and a separator that maintains electrical insulation between the polarizable electrodes. As the electrolytic solution, an aqueous solution such as sulfuric acid or an organic solvent using a quaternary ammonium salt as a supporting salt is used. Since the capacitance of such an electric double layer capacitor is proportional to the surface area of the polarizable electrode, the polarizable electrode is usually a molded product of activated carbon or activated carbon fiber having a high surface area. The electric double layer has a capacity of several tens of μF per 1 cm ² , but an extremely large capacity of several hundred to several thousand F can be obtained by using a carbon electrode having a high surface area of several thousand to several tens of thousands m ^2. Is possible.

However, the energy density of a general electric double layer capacitor is currently about 5 to 8 Wh / kg, whereas, for example, a lithium ion battery is currently 100 to 150 Wh / kg, and a NAS battery is currently 100 to 120 Wh / kg. kg and has a capacity 20 to 30 times or more that of an electric double layer capacitor. This is a difference that cannot be overcome only by improvements such as increasing the surface area of the polarizable electrode used or changing the supporting salt of the electrolyte. Therefore, even if the volume is increased by increasing the volume, it can be said that the secondary battery is not suitable for use in full-scale power storage because the energy density is too low.

On the other hand, the inventors of the present invention, in an electric double layer capacitor that operates at a high temperature using a molten salt such as an alkali halide as an electrolytic solution, is extremely compared with a case where it is operated at room temperature using an aqueous solution such as sulfuric acid or an organic solvent. It has been confirmed that a large capacity can be expressed, and there is a report that the electrostatic capacity can be increased to 10 times or more (for example, Patent Document 1).

Therefore, a high-temperature operation type electric double layer capacitor using a molten salt as an electrolytic solution has an energy density comparable to that of the above-described lithium ion battery or a NAS battery operated in a high temperature region of 300 to 350 ° C. It can be used for full-scale power storage.

On the other hand, there is a thermal battery as a high-temperature operation type battery using the molten salt. A thermal battery is a battery that uses calcium chromate or iron disulfide as a positive electrode active material, calcium or lithium as a negative electrode active material, and a molten salt such as lithium chloride-potassium chloride as an electrolyte. A thermal battery is a type of storage battery, and unless the electrolyte salt melts, the battery reaction does not proceed, and there is practically no self-discharge during storage. 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.

In addition, since the thermal battery operates at a high temperature, the electrode reaction proceeds much faster than a battery operated at room temperature using an aqueous solution, an organic solvent, or the like, and thus has excellent large current discharge characteristics. Taking advantage of these characteristics, it is suitably used as a power source for emergency development and various defense equipment such as space development-related equipment used in rockets and induction equipment.

However, in recent years, with the improvement in the performance of the above-described devices, there is a demand for the development of a thermal battery that can withstand the use of a plurality of times (improved energy density and thermal battery).

The capacity of the thermal battery is about 10 Wh / kg for the calcium type and about 40 Wh / kg for the lithium type, and it is considered that no further significant improvement can be expected. In some cases, the lithium / iron sulfide thermal battery can be recharged by an external power source. However, a thermal battery that can withstand repeated charging and discharging like a normal secondary battery has not yet been developed.

In contrast, an electric double layer capacitor using a molten salt as an electrolyte solution has a high energy density that can be used for large-scale power storage as described above, a high output characteristic peculiar to an electric double layer capacitor, and a high cycle life. Therefore, it is highly possible to match the use of the thermal battery as a power device that greatly exceeds the performance of the thermal battery.

However, in conventional high temperature operation type capacitors using molten salt, it was considered necessary to always keep the electrolyte salt in a molten state when using this capacitor. It has never been applied to pulse storage such as power storage and thermal battery applications.
JP-A-5-136002

Therefore, the present invention can be applied to a high-temperature operation type capacitor using a molten salt for a pulsed use such as short-term to long-term large-scale power storage and thermal battery use, and It is an object of the present invention to provide a thermally activated molten salt capacitor that can arbitrarily take out electrical energy stored in a capacitor when needed.

In the high-temperature operation type capacitor using such a molten salt, the inventors of the present invention maintained a state where charging was completed, and when the molten salt as an electrolyte was cooled and solidified, the salt solidified by heating again. It was found that the state of charge before solidification was maintained even when the was melted again, and the thermally activated molten salt capacitor of the present invention was completed.

The operating principle and structure of the heat start type molten salt capacitor in the present invention is the same as that of an electric double layer capacitor using a general molten salt, and while the electrolyte salt is in a molten state, it is large in the normal high temperature operation type. Operates as a capacitive capacitor.

Here, when the electrolyte salt is cooled while maintaining the charged state, the salt solidifies while maintaining the structure of the charged electric double layer. When heating again, the electrolyte salt melts while maintaining the charged state, so that the charged power can be taken out when necessary.

Since the electrolyte salt is not conductive while the electrolyte salt is solid at room temperature, the device itself is inactive and can withstand long-term storage in the same way as a thermal battery. In most cases, a thermal battery is disposable after being used once, but a heat-activated molten salt capacitor can be recharged and reused as many times as the device can be recovered.

In addition, the know-how related to packaging, which is a problem when selecting the material used for the device, solidifying, and remelting, can be diverted from everything obtained in the development of thermal batteries. For example, it is currently manufactured as a thermal battery. However, it can be used as a thermally activated molten salt capacitor by replacing only the electrode portion with a porous carbon electrode.

In other words, according to the present invention, a revolutionary power storage that combines the high power storage capability and high output characteristics of an electric double layer capacitor using a molten salt, and the ability to store power efficiently over a long period of time, such as a thermal battery. The device can be manufactured.

Specifically, the invention described in claim 1 is a thermally activated molten salt capacitor formed by a pair of polarizable electrodes and an electrolyte interface made of a molten salt, and stores electric energy in the capacitor. The capacitor is characterized in that the molten salt is solidified in a wet state. The invention according to claim 2 is a thermally activated molten salt capacitor formed by a pair of polarizable electrodes and an electrolyte interface made of a molten salt, and the molten salt accumulates electric energy in the capacitor. The capacitor is solidified in a state in which the molten salt is solidified, and the stored electric energy can be taken out by remelting the molten salt.

According to the first and second aspects of the present invention, the operating principle and structure of the thermally activated molten salt capacitor is the same as that of an electric double layer capacitor using a general molten salt, so that the electrolyte salt is in a molten state. In the meantime, it operates as a normal high-temperature operation type large capacity capacitor. However, when the electrolyte salt is cooled while maintaining the charged state, the electrolyte salt is solidified while maintaining the structure of the charged electric double layer. Therefore, when heating again, the electrolyte salt melts while maintaining the charged state, so that the charged power can be taken out when necessary.

That is, in the thermally activated molten salt capacitor according to the present invention, as long as the device can be recovered, it can be recharged and reused any number of times. The high power storage capability and high output characteristics of the electric double layer capacitor using the molten salt, and An electric power storage device having a capability of storing electric power with high efficiency even for a long time like a thermal battery can be manufactured.

A third aspect of the present invention is the capacitor according to the first or second aspect, wherein a separator is disposed in the electrolyte of the capacitor in order to prevent a short circuit between the polarizable electrodes.

According to the third aspect of the present invention, even when the distance between the pair of polarizable electrodes is very narrow, a short circuit between the polarizable electrodes due to contact can be prevented. It is possible to provide a thermally activated molten salt capacitor having the above.

According to the invention described in claim 4, the molten salt includes an alkali metal halide, an alkaline earth metal halide, an alkali metal carbonate, an alkaline earth metal carbonate, an alkali metal sulfate, an alkaline earth metal sulfate, an alkali. 4. The capacitor according to claim 1, wherein one or more compounds selected from metal nitrates and alkaline earth metal nitrates are used. In addition, as a further preferred example of the invention described in claim 4, the invention described in claim 5 includes alkali metal halides such as LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl. 5. The capacitor according to claim 4, wherein one or more compounds selected from LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, and CsI are used.

According to the fourth and fifth aspects of the present invention, it is possible to provide a thermally activated molten salt capacitor capable of extremely stable charge and discharge even when the molten salt that is an electrolyte is repeatedly solidified and remelted. .

The invention described in claim 6 is characterized in that an alkali metal halide having a composition ratio of LiCl: KCl = 35 mol% to 100 mol%: 65 mol% to 0 mol% is used as the molten salt. It is. Further, the invention according to claim 7 is an alkali metal halide having a composition ratio of LiCl: KCl = 55 mol% to 65 mol%: 45 mol% to 35 mol% as a more preferable example of the invention according to claim 6. The capacitor according to claim 6, wherein the capacitor is used.

According to the inventions described in claims 6 and 7, when the molten salt and the polarizable electrode are sufficiently adapted to each other, an extremely large amount of charge can be accumulated, and charging / cooling and melting / discharging cycles can be performed. It is possible to provide a thermally activated molten salt capacitor that can generate a stable voltage even when it is repeated, and has excellent cycle characteristics.

The invention described in claim 8 is that an alkali metal halide having a composition ratio of LiCl: KCl: CsCl = 55 mol% to 65 mol%: 10 mol% to 15 mol%: 20 mol% to 30 mol% is used as the molten salt. 7. The capacitor according to claim 6, wherein the molten salt having this composition ratio can be operated at a lower temperature because of its low melting point.

The invention described in claims 9 and 10 is another preferable example of the invention described in claims 6 and 7 described above. Among these, the invention described in claim 9 is characterized in that an alkali metal halide having a composition ratio of LiBr: KBr = 35 mol% to 100 mol%: 65 mol% to 0 mol% is used as the molten salt. According to a tenth aspect of the present invention, there is provided a molten salt having a composition ratio of LiBr: KBr = 60 mol% to 70 mol%: 40 mol% to 30 mol% as a further preferred example of the invention according to the ninth aspect. The capacitor according to claim 9, wherein an alkali metal halide is used.

According to the ninth and tenth aspects of the invention, similar to the sixth and seventh aspects of the invention, the molten salt and the polarizable electrode are sufficiently adapted to accumulate a very large amount of charge. In addition, it is possible to provide a thermally activated molten salt capacitor excellent in cycle characteristics that can generate a stable voltage even when charging / cooling and melting / discharging cycles are repeated.

The invention according to claim 11 is the use of an alkali metal halide having a composition ratio of LiBr: KBr: CsBr = 50 mol% -60 mol%: 15 mol% -20 mol%: 20 mol% -30 mol% in the molten salt. 7. The capacitor according to claim 6, wherein the molten salt having this composition ratio can be operated at a lower temperature because of its low melting point.

The invention according to claim 12, the alkaline earth metal _{halides, MgF 2, CaF 2, SrF} 2, BaF 2, MgCl 2, CaCl 2, SrCl 2, BaCl 2, MgBr 2, CaBr 2, SrBr 2, BaBr _2, a _{MgI 2, CaI 2, SrI 2} , capacitor according to claim 4, characterized by using one or more compounds selected from BaI _2.

According to the invention described in claim 12, similarly to the invention described in claim 5, even when solidification and remelting of the molten salt that is an electrolyte are repeated, thermal start-up capable of extremely stable charge and discharge is possible. Type molten salt capacitor can be provided.

According to the invention of any one of claims 13 to 15, there is provided the capacitor according to any one of claims 1 to 3, wherein an onium salt of nitrogen having a melting point of 40 ° C. or higher is used as the molten salt. .

1. Thermally activated molten salt capacitor Details of the thermally activated molten salt capacitor according to the present invention will be described below. The heat-start type molten salt capacitor according to the present invention is not particularly limited as to the heat source in the case of restarting, and those having less supply fluctuation such as factory waste heat can be used, but preferably the supply heat amount such as solar heat is periodic. It is preferable to use a disposable heat source such as one that changes to 1 or a heat pellet (a mixture of iron powder and potassium perchlorate) used in a thermal battery.

There is no restriction | limiting in particular also about the activation time at the time of making it restart, What is necessary is just to determine suitably according to the capacity | capacitance of the capacitor to be used, the kind of electrolyte salt, or the urgency of electric power necessity.

The structure of the thermally activated molten salt capacitor is not particularly limited, and may be used as a single cell or may be stacked in series according to the required output voltage.

When the electrolyte salt is solidified and stored for a long period of time, it must be kept airtight so that the electrolyte salt does not absorb moisture. This is also the same as the conventional thermal battery. The entire cell may be held in a cup like a cup battery often found in thermal batteries, or battery components may be pelletized like a pellet battery.

2. Polarized electrode As the polarizable electrode, powdered normal activated carbon is mixed with an appropriate binder and molded by press molding or rolling roll, or activated carbon such as phenol, rayon, pitch, etc. Felt and paper made of fiber, porous metal (for example, Raney metal), rare earth oxide, and carbon coated on a conductive substrate by vapor deposition or molten salt plating can be used. It is preferable to use molten salt-plated carbon obtained in a state filled with salt. However, materials that cause a chemical reaction with the molten salt to be used, are eluted during charging / discharging, or deteriorate due to the heat of the molten salt cannot be used.

When the electrolyte salt is cooled, it is solidified while maintaining the state where the charging is completed. This cooling process may be performed while maintaining the voltage between the two polarizable electrodes during charging, or may be performed in an open circuit state after completion of charging. However, the former method is preferable in order to prevent loss of stored power due to the self-discharge phenomenon in the open circuit state except when cooling in a single time such as several tens of seconds to several minutes.

In order to prevent the two polarizable electrodes from coming into contact with each other and causing a short circuit, the polarizable electrodes are opposed to each other with a predetermined interval, for example, by sandwiching an insulating separator between the polarizable electrodes.

As the separator, a material that does not cause chemical reaction with molten salt or deterioration due to heat in the operating temperature range is preferable. For example, porous alumina, silica, etc., and in order to keep internal resistance as low as possible, It is desirable to use a thin one.

Molten salt The molten salt used as the electrolyte in the high-temperature operating capacitor of the present invention is usually an alkali metal halide, alkaline earth metal halide, alkali metal carbonate, alkaline earth metal carbonate, alkali metal. Sulfates, alkaline earth metal sulfates, alkali metal nitrates, alkaline earth metal nitrates and the like are used, and alkali metal halides and alkaline earth metal halides are particularly preferable.

As the alkali metal halide, LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, CsI, etc. can be used. Examples of the alkaline earth metal _{halide, MgF 2, CaF 2, SrF} 2, BaF 2, MgCl 2, CaCl 2, SrCl 2, BaCl 2, MgBr 2, CaBr 2, SrBr 2, BaBr 2, MgI 2, CaI ₂ , SrI ₂ , BaI _{2 and the} like can be used.

The said compound can also be used independently and can also be used in combination of 2 or more type. A combination of these compounds, the number of compounds to be combined, a mixing ratio, and the like are not limited, and can be appropriately selected according to a preferable operating temperature range.

In the present invention, LiCl and / or KCl melted (LiCl: KCl = about 35 mol% to 100 mol%: about 65 mol% to 0 mol%, preferably about 55 mol% to 65 mol%: about 45 mol% to 35 mol%) , LiCl, KCl, and CsCl melted (LiCl: KCl: CsCl = 57.5: 13.3: 29.2 mol% is preferable, but the composition ratio may be changed by about 20% each. ), LiBr and / or KBr melted (LiBr: KBr = about 35 mol% to 100 mol%: about 65 mol% to 0 mol%, preferably about 60 mol% to 70 mol%: about 40 mol% to 30 mol%), LiBr, What melted KBr and CsBr (LiBr: KBr: sBr = 56.1: 18.9: Although 25.0 mol% of the eutectic composition is preferred, the composition ratio may be obtained by changing each about 20%) are preferred.

In the field of electrochemistry, “molten salt” means a salt that is not dissociated into ions in the solid state but dissociates into ions in the molten state. In this sense, the “molten salt” includes not only the inorganic molten salt described so far, but also the onium salt of nitrogen that has been actively studied in recent years. Nitrogen onium salts include tetraalkylammonium salts, imidazolium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, and the like depending on the structure of the cation moiety. Molten salts of nitrogen onium salts (sometimes referred to as “quaternary ammonium salts, etc.” below) are being studied actively at room temperature molten salts, also known as ionic liquids, used as electrolytes for lithium secondary batteries. is there. In this case, it is a necessary condition that it is liquid at room temperature, which is the use temperature of the battery. However, in the case of the thermally activated molten salt capacitor of the present invention, it is a necessary condition that it is solid at ordinary temperature. For this reason, the quaternary ammonium salt or the like is selected from those having a melting point of 40 ° C. or higher, preferably 60 ° C. or higher, and most preferably 80 ° C. or higher.

Such quaternary ammonium salts are preferably composed of cations and anions exemplified below, but are not limited thereto.

Cation:
1,3-dimethylimidazolium (DMI),
1-ethyl-3-methylimidazolium (EMI),
1-butyl-3-methylimidazolium (BMI),
1-allyl-3-methylimidazolium (AEI),
1-allyl-3-butylimidazolium (ABI),
1,3-diallylimidazolium (AAI),
1,2-dimethyl-3-benzylimidazolium,
1-ethyl-2-methyl-3-benzylimidazolium,
1-tetradecyl-3-methylimidazolium,
1-hexadecyl-3-methylimidazolium,
1-octadecyl-3-methylimidazolium,
1-ethyl-2,3-dimethylimidazolium,
1-butyl-2,3-dimethylimidazolium,
1-hexyl-2,3-dimethylimidazolium,
1-ethylpyridinium,
1-butylpyridinium,
1-hexylpyridinium,
1-butyl-3-methylpyridinium,
1-butyl-4-methylpyridinium,
1-butyl-3,4-dimethylpyridinium,
1-butyl-3,5-dimethylpyridinium,
N, N-diethyl-N-methyl-N- (2-methoxyethyl) ammonium,
N, N, N-trimethyl-N-propylammonium,
Methyltrioctylammonium,
1-methyl-1-propylpiperidinium,
1-methyl-1-propylpyrrolidinium,
1-butyl-1-methylpyrrolidinium 1-hexyl-1-methylpyrrolidinium 1-octyl-1-methylpyrrolidinium and the like.

Anion:
F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , BF ₄ ⁻ , Pf ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ^−, ie, bis (trifluoromethylsulfonyl) imide (TFSI), perfluoro substituted with fluorine Aliphatic, alicyclic or aromatic sulfonates, aliphatic, alicyclic or aromatic carboxylates that can be substituted with fluorine up to perfluoro, and the like.

Preferred specific examples of imidazolium salts having a melting point of 40 ° C. or higher include 1-ethyl-3-methylimidazolium chloride (EMICl: mp = 78 ° C.), bromide (mp = 74 ° C.), methanesulfonate (mp = 40 ° C.) and Hexafluorophosphate (mp = 62 ° C.), 1-butyl-3-methylimidazolium (BMI) chloride (mp = 73 ° C.), bromide (mp = 57 ° C.) and methanesulfonate (mp = 77 ° C.), 1,2 -Dimethyl-3-benzylimidazolium iodide (mp = 153.5 ° C.), 1-ethyl-2-methyl-3-benzylimidazolium iodide (mp = 115 ° C.), 1-hexadecyl-3-methylimidazolium Chloride (mp = 65 ° C.), 1-octadecyl-3-methylimidazolium chloride ( mp = 71 ° C.), 1,3-dimethylimidazolium trifluoromethanesulfonate (mp = 43 ° C.), 1-allyl-3-ethylimidazolium bromide (mp = 55 ° C.), 1-butyl-2,3-dimethylimidazole Rium bromide (mp = 105 ° C.), chloride (mp = 102 ° C.), 1-ethyl-2,3-dimethylimidazolium bromide (mp = 141 ° C.), 1-hexyl-2,3-dimethylimidazolium chloride (mp = 62 ° C.), but is not limited thereto.

Examples of tetraalkylammonium quaternary salts having a melting point of 40 ° C. or higher are tetramethylammonium TFSI (mp = 133 ° C.), tetraethylammonium TFSI (mp = 109 ° C.), and tetra-n-propylammonium TFSI (mp = 105 ° C.). , Tetra-n-butylammonium TFSI (mp = 96 ° C.), N, N-diethyl-N, N-di-isopropylammonium TFSI (mp = 148 ° C.), N-methyl-N-ethyl-N, N-di -Isopropylammonium TFSI (mp = 140 ° C), N-heptyl-N, N, N-trimethylammonium trifluoromethanemethanesulfonate (mp = 140 ° C), N-hexyl-N, N, N-tributylammonium trifluoromethanesulfonate ( mp = 72 ° C.), cetyldimethylethyl Ammonium bromide (mp = 178~186 ℃), and the like.

Examples of pyridinium type quaternary salts include 1-hexadecylpyridinium perfluorobutane sulfonate (mp = 95 ° C.), 1-hexadecyl pyridinium paratoluene sulfonate (mp = 138 ° C.), and the like.

The temperature to be set varies depending on the type of salt to be used and the polarizable electrode, but may be any temperature that maintains a low viscosity so that the molten salt penetrates into the polarizable electrode and diffuses into the pores. Further, the applied voltage at the time of charging must be equal to or lower than the decomposition voltage of the molten salt to be used. Therefore, it is desirable that the salt type, combination and composition have a high decomposition voltage.

According to the present invention, in a high temperature operation type capacitor using a molten salt, when the molten salt that is an electrolyte is cooled and solidified while maintaining a state where charging is completed, the salt solidified by heating again is re-applied. Utilizing the property based on the new knowledge of maintaining the state of charge before solidification even when melted, it can be used for short-term to long-term large-scale power storage and pulsed use such as thermal battery applications. It is possible to provide a thermally activated molten salt capacitor that can be applied and can arbitrarily take out the electrical energy stored in the capacitor when needed.

Embodiments of the present invention will be described below with reference to the drawings. The present invention is not limited to the examples shown below, and various modifications can be made without departing from the technical idea of the present invention.

FIG. 1 shows an experimental operation of Example 1 simulating a heat-started molten salt capacitor according to the present invention in order to investigate the polarization behavior of one electrode. An embodiment in which an electrolyte made of a molten salt is solidified in a state where electric energy is accumulated, or a solidified electrolyte is redissolved is shown.

In a glove box under an argon atmosphere, LiCl—KCl mixed with a eutectic composition was heated to 400 ° C. and melted, and then this was used as an electrolyte 10 to examine high-temperature capacitor characteristics before and after cooling and solidification. As a working electrode, a porous carbon film electrode 11 produced by molten salt plating on an Al substrate is used, a glassy carbon is used for the counter electrode 12, an Ag ⁺ / Ag electrode is used for the reference electrode 13, and a three-electrode system is used. Measurements were made.

Cathode-anode constant current electrolysis at ± 50 mA (1,285 mAg ⁻¹ ) was alternately and repeatedly performed in a potential region of 1.1 V to 1.5 V on the basis of the Li ⁺ / Li potential. FIG. 2 shows the measurement result of the open circuit electrode potential during repetition of charging and discharging at ± 50 mA. During the open circuit potential measurement, the carbon electrode 11 was once lifted from the bath, After confirming that the attached electrolyte salt 10 has solidified, an operation of inserting it again into the bath 10 is performed.

After the start of the measurement of the open circuit potential, there is a slight change in potential that can be attributed to self-discharge. Here, since the carbon electrode 11 is pulled up from the bath 10, the measurement is temporarily interrupted. The potential of the carbon electrode 11 after being inserted into the bath 10 again showed the same value as before the pulling, and the discharge could be performed thereafter. From this result, even when the bath 10 is pulled up, the structure of the electric double layer at the time of completion of charging is maintained, and the structure does not change as long as it is an open circuit even after the process of cooling solidification and remelting. I understood.

FIG. 3 shows the relationship between the respective capacities during charging and discharging and the number of cycles for the results of FIG. From the second cycle onward, the capacity is stable and continues to show an extremely large value of about 230 Fg ^−1, and there is no effect of solidifying the electrolyte salt by taking it out from the bath 10 during charging / discharging.

FIG. 4 shows the relationship between charge / discharge efficiency and the number of cycles. In the first cycle, since the electrode 11 is not sufficiently familiar with the molten salt 10, the charge / discharge efficiency is a slightly small value, but after the second cycle, the value is almost 100%.

FIG. 5 shows an experimental operation of Example 2 that approximates a thermally activated molten salt capacitor according to the present invention, and is composed of a molten salt in a state where electric energy is accumulated in the capacitor and in a state where electric energy is accumulated. An embodiment in which the electrolyte is solidified or the solidified electrolyte is redissolved is shown.

As is apparent from FIG. 5, in Example 2, a cell having the same electrolyte and the same structure as in Example 1 was prepared using the same two carbon electrodes 11 as the molten salt plating used in Example 1. And measured.

FIG. 6 shows the voltage change between the electrodes when charging / discharging at ± 50 mA. Here again, as in Example 1, the carbon electrode was measured during open circuit voltage measurement between repeated charging and discharging. 11 is pulled up from both baths, and after confirming that the electrolyte salt 10 has solidified, the operation of inserting it again into the bath 10 is repeated.

Similar to the result of Example 1, the voltage between the carbon electrodes 11 after being inserted into the bath 10 again remained substantially the same value, and it was confirmed that there was no potential change during the solidification of the electrolyte salt. . The same charging and discharging operations were performed for 5 cycles, but almost the same behavior was exhibited. From this, it was confirmed that even when the bath 10 was pulled up, the electric double layer structure at the time of completion of charging was maintained, and this did not change even after cooling solidification and remelting.

FIG. 7 shows the relationship between the single-electrode capacity during charging and discharging and the number of cycles for the results shown in FIG. From the third cycle onward, the capacity is stable and continues to show a very large value of about 210 Fg ^−1, and the effect of solidifying the electrolyte salt by removing the electrode pair of the carbon electrode 11 from the bath 10 during charging and discharging. Is not seen at all.

FIG. 8 shows the relationship between charge / discharge efficiency and the number of cycles. Up to the second cycle, since the electrode 11 was not sufficiently familiar with the molten salt 10, the charge / discharge efficiency was a slightly small value, but after the third cycle, the value was almost 100%.

  A cell having the same structure as in Example 2 except that 1-ethyl-3-methylimidazolium chloride (EMICl) melted at 100 ° C. is used as an electrolyte, two carbon electrodes made of activated carbon fibers are used as electrodes, Was made and measured.

  FIG. 9 shows the voltage change between the electrodes when charging / discharging at ± 10 mA. Here again, as in Example 2, the carbon electrode was measured during open circuit voltage measurement between charging and discharging. Both the electrodes are lifted from the bath, and after confirming that the electrolyte salt has solidified, the operation of inserting it again into the bath is repeated.

  Similar to the result of Example 1, the voltage between both electrodes of the carbon electrode 11 after being inserted into the bath again maintained substantially the same value, and it was confirmed that there was no potential change during the solidification of the electrolyte salt. The same charging and discharging operations were performed for 5 cycles, but almost the same behavior was exhibited. Therefore, even when EMICl is used as the electrolyte, the electric double layer structure at the time of completion of charging is maintained in the state where the electrolyte is pulled up from the bath, and this does not change even after cooling solidification and remelting. It was confirmed.

FIG. 10 shows the relationship between the single-electrode capacity during charging and discharging and the number of cycles for the results shown in FIG. The capacity is stable around 80 Fg ⁻¹ , and there is no effect of solidifying the electrolyte salt by removing the electrode pair of the carbon electrode from the bath during charging and discharging.

  FIG. 11 shows the relationship between charge / discharge efficiency and the number of cycles. The charge / discharge efficiency is stable at a value of about 80%, and there is no significant change. The charge / discharge efficiency was a relatively low value, which is due to the influence of impurities such as moisture remaining in the molten salt. In order to maintain a large charge / discharge capacity and high charge / discharge efficiency, it is necessary to sufficiently remove impurities such as moisture in advance.

The thermally activated molten salt capacitor of the present invention has a cell structure as shown in FIG. 12, for example, and can be applied to pulsed uses such as short-term to long-term large-scale power storage and thermal battery applications. Therefore, it can be used in a wide range of equipment that requires a power source, such as space development-related equipment, induction equipment, and emergency power supplies.

In order to investigate the polarization behavior of the electrode on one side, a mode in which electric energy is accumulated in the capacitor and a mode in which the electrolyte made of molten salt is solidified or the solidified electrolyte is re-dissolved in the state where the electric energy is accumulated are shown. It is sectional drawing which shows the structure outline | summary of Example 1 which simulated the heat starting type molten salt capacitor by this invention. FIG. 2 shows the cathode-anode constant current electrolysis at ± 50 mA (1,285 mAg ⁻¹ ) alternately in the potential region of 1.1 V to 1.5 V with respect to the Li ⁺ / Li potential in the capacitor of Example 1. Shows the measurement results of the open circuit electrode potential when it is repeatedly performed. FIG. 3 shows the relationship between the respective capacities during charging and discharging and the number of cycles for the results of FIG. FIG. 4 shows the relationship between the charge / discharge efficiency and the number of cycles for the results of FIG. Approximate the heat-starting molten salt capacitor according to the present invention, which shows a mode in which electric energy is stored in the capacitor and a mode in which the electrolyte made of molten salt is solidified or the solidified electrolyte is re-dissolved in the state where electric energy is stored It is sectional drawing which shows the structure outline | summary of Example 2 made. FIG. 6 shows the voltage change between the electrodes when the capacitor of Example 2 is charged and discharged at ± 50 mA. FIG. 7 shows the relationship between the respective capacities during charging and discharging and the number of cycles for the results of FIG. FIG. 8 shows the relationship between the charge / discharge efficiency and the number of cycles for the result of FIG. FIG. 9 shows the voltage change between the electrodes when the capacitor of Example 3 is charged and discharged at ± 10 mA. FIG. 10 shows the relationship between the respective capacities during charging and discharging and the number of cycles for the results of FIG. FIG. 11 shows the relationship between the charge / discharge efficiency and the number of cycles for the result of FIG. It is the schematic which expanded partially the cross section of the cell structure of the heat start type molten salt capacitor by this invention.

Explanation of symbols

1, 2 ... Thermally activated molten salt capacitor 10 ... Molten salt LiCl-KCl
11 .... carbon electrode 12 .... counter electrode 13 .... reference electrode 14 .... electrochemical measuring device

Claims (15)

A thermally activated molten salt capacitor formed by a pair of polarizable electrodes and an electrolyte interface made of a molten salt,
The capacitor characterized in that the molten salt is solidified in a state where electric energy is accumulated in the capacitor. A thermally activated molten salt capacitor formed by a pair of polarizable electrodes and an electrolyte interface made of a molten salt,
The capacitor, wherein the molten salt is solidified in a state where electric energy is accumulated in the capacitor, and the accumulated electric energy can be taken out by remelting the molten salt.   The capacitor according to claim 1, wherein the capacitor includes a separator for preventing a short circuit between polarizable electrodes.   The molten salt is alkali metal halide, alkaline earth metal halide, alkali metal carbonate, alkaline earth metal carbonate, alkali metal sulfate, alkaline earth metal sulfate, alkali metal nitrate, alkaline earth metal nitrate The capacitor according to claim 1, comprising one or more compounds selected from the group consisting of:   The alkali metal halide was selected from LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, CsI. The capacitor according to claim 4, wherein the capacitor is one or more compounds.   The capacitor according to claim 5, wherein the molten salt contains an alkali metal halide having a composition ratio of LiCl: KCl = 35 mol% to 100 mol%: 65 mol% to 0 mol%.   The capacitor according to claim 6, wherein the molten salt contains an alkali metal halide having a composition ratio of LiCl: KCl = 55 mol% to 65 mol%: 45 mol% to 35 mol%.   The molten salt contains an alkali metal halide having a composition ratio of LiCl: KCl: CsCl = 55 mol% to 65 mol%: 10 mol% to 15 mol%: 20 mol% to 30 mol%. Capacitor.   The capacitor according to claim 5, wherein the molten salt contains an alkali metal halide having a composition ratio of LiBr: KBr = 35 mol% to 100 mol%: 65 mol% to 0 mol%.   10. The capacitor according to claim 9, wherein the molten salt contains an alkali metal halide having a composition ratio of LiBr: KBr = 60 mol% to 70 mol%: 40 mol% to 30 mol%.   The molten salt includes an alkali metal halide having a composition ratio of LiBr: KBr: CsBr = 50 mol% to 60 mol%: 15 mol% to 20 mol%: 20 mol% to 30 mol%. Capacitor. The alkaline earth metal _{halides, MgF 2, CaF 2, SrF} 2, BaF 2, MgCl 2, CaCl 2, SrCl 2, BaCl 2, MgBr 2, CaBr 2, SrBr 2, BaBr 2, MgI 2, CaI 2 5. The capacitor according to claim 4, wherein the capacitor is one or more compounds selected from SrI ₂ and BaI ₂ .   The capacitor according to claim 1, wherein the molten salt is an onium salt of nitrogen having a melting point of 40 ° C. or higher.   14. The capacitor according to claim 13, wherein the cation of the onium salt of nitrogen is a tetraalkylammonium, imidazolium, piperidinium, pyrrolidinium, or pyridinium cation. The anion of the onium salt of nitrogen is a halide anion, BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , an aliphatic, alicyclic or aromatic sulfonate anion that can be substituted with fluorine up to perfluoro 15. A capacitor according to claim 13 or 14, which is an aliphatic, alicyclic or aromatic carboxylate anion that can be substituted with fluorine up to perfluoro.

Images