KR20160003384A - Electrolyte for Sodium Secondary Battery and Sodium Secondary Battery using thereof - Google Patents

Abstract

The present invention relates to an electrolyte for a sodium secondary battery, and a sodium secondary battery applying the same and, more specifically, to a sodium secondary battery comprising a negative electrode containing sodium, a positive electrode comprising transition metal and metal selected from group 12 to 14, and a sodium ion-conductive solid electrolyte formed between the negative electrode and the positive electrode, wherein the positive electrode is impregnated in the electrolyte containing one or more kind of organic compounds and sodium molten salt.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolyte for a sodium secondary battery and a sodium secondary battery employing the electrolyte.

The present invention relates to an electrolyte for a sodium secondary battery and a sodium secondary battery employing the same.

With the rapid increase in the use of renewable energy, the need for battery-powered energy storage devices is increasing rapidly. Among such batteries, a lead battery, a nickel / hydrogen battery, a vanadium battery, and a lithium battery can be used. However, the lead and nickel / hydrogen batteries have a very low energy density, which requires a lot of space to store the same amount of energy. In addition, in the case of vanadium batteries, there is a problem in that performance is deteriorated due to environmental pollution caused by the use of a solution containing heavy metals and a small amount of material moving between the cathode and the anode through the membrane separating the cathode and the anode. It can not be commercialized. Lithium batteries having excellent energy density and output characteristics are technically very advantageous. However, due to the scarcity of resources of lithium materials, they are not economically feasible to be used as a large-scale power storage secondary battery.

In order to solve these problems, there have been many attempts to utilize the abundant sodium on the earth as a resource of a secondary battery.

Among them, as disclosed in U.S. Patent Publication No. 20030054255, a sodium-sulfur battery in which beta-alumina having selective conductivity for sodium ions is used, sodium is used for a cathode and sulfur is used for an anode is currently used as a large-scale power storage device .

However, existing sodium-based secondary batteries, such as sodium-sulfur batteries or sodium-nickel chloride batteries, must operate above 250 ° C minimum in the case of sodium-nickel chloride batteries, taking into account the melting point of the conductivity and battery composition, In the case of a sodium-sulfur battery, it has an operating temperature of at least 300 ° C. Due to these problems, there are many disadvantages in terms of manufacturing or operational economics in order to enhance the maintenance of temperature, the maintenance of airtightness, and the safety.

In order to solve the above problems, room temperature type sodium-based batteries have been developed, but their output is very low and their competitiveness is lower than that of a nickel-hydrogen battery or a lithium battery.

U.S. Published Patent Application 20030054255

The electrolyte for a sodium secondary battery according to the present invention is to provide an electrolyte in which an organic compound is added to a sodium molten salt to thereby lower the melting point. At the same time, it is intended to provide an electrolyte capable of driving a battery without a drastic decrease in ion conductivity, while a melting point is lowered.

In addition, the sodium secondary battery according to the present invention employs an electrolyte having a lower melting point than that of the conventional sodium molten salt electrolyte, and can operate at a low temperature, is prevented from deterioration, improves the life of the battery, To provide a non-explosive sodium secondary battery.

Another object of the present invention is to provide a sodium secondary battery capable of operating at a low temperature to reduce manufacturing costs and ensure stability.

The electrolyte for a sodium secondary battery according to the present invention comprises 99.9 to 80 wt% of a sodium molten salt and 0.1 to 20 wt% of a nitrile organic compound.

In the electrolyte for a sodium secondary battery according to an embodiment of the present invention, the nitrile organic compound may be one or more selected from adiponitrile, succinonitrile and sebaconitrile.

In an electrolyte for a sodium secondary battery according to an embodiment of the present invention, the sodium molten salt may be sodium aluminum chloride.

The electrolyte for a sodium secondary battery according to an embodiment of the present invention may have a melting point of 150 ° C or less as described above.

The electrolyte for a sodium secondary battery according to an embodiment of the present invention may have an ionic conductivity of 200 ms / cm or more upon melting.

On the other hand, a sodium secondary battery employing the above-described electrolyte for a sodium secondary battery can be manufactured.

Specifically, the sodium secondary battery according to the present invention comprises a negative electrode containing sodium, a positive electrode containing a metal selected from a transition metal, and a sodium ion conductive solid electrolyte provided between the negative electrode and the positive electrode, 99.9 to 80 wt% of a molten salt of sodium and 0.1 to 20 wt% of a nitrile organic compound are impregnated into an electrolyte for a sodium secondary battery.

In the sodium secondary battery according to an embodiment of the present invention, the nitrile organic compound may be one or more selected from adiponitrile, succinonitrile, and sebaconitrile.

In a sodium secondary battery according to an embodiment of the present invention, the sodium molten salt may be sodium aluminum chloride.

In the sodium secondary battery according to an embodiment of the present invention, the electrolyte may have a melting point of 150 ° C or less.

In the sodium secondary battery according to an embodiment of the present invention, the electrolyte may have an ion conductivity of 200 ms / cm or more upon melting.

In the sodium secondary battery according to an embodiment of the present invention, the cathode may include molten sodium.

In the sodium secondary battery according to an embodiment of the present invention, the anode may include a metal selected from one or more of nickel, copper, iron, manganese, cobalt, and alloys thereof.

The sodium secondary battery according to an embodiment of the present invention can be operated at an operating temperature range of 120 to 200 ° C. by adopting the above configuration.

INDUSTRIAL APPLICABILITY The sodium secondary battery according to the present invention employs an electrolyte having a lower melting point than that of a conventional sodium molten salt electrolyte and is capable of operating at a low temperature and preventing deterioration, thereby improving the lifetime of the battery and exhibiting high ionic conductivity, There is an advantage of having non-explosive properties.

In addition, the sodium secondary battery according to the present invention is advantageous in that it can be operated at a low temperature, thereby reducing manufacturing cost and securing stability.

1 is a conceptual view schematically showing a structure of a sodium secondary battery according to an embodiment of the present invention.
2 is a graph showing a result of cyclic voltammetry of a sodium secondary battery manufactured according to an embodiment of the present invention.

Hereinafter, a sodium secondary battery according to the present invention will be described in detail with reference to the accompanying drawings.

The following drawings are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention. Therefore, the present invention is not limited to the following drawings, but may be embodied in other forms, and the following drawings may be exaggerated in order to clarify the spirit of the present invention. Also, throughout the specification, like reference numerals designate like elements.

Hereinafter, the technical and scientific terms used herein will be understood by those skilled in the art without departing from the scope of the present invention. Descriptions of known functions and configurations that may be unnecessarily blurred are omitted.

In general, a sodium aluminum chloride (NaAlCl ₄ ) molten salt electrolyte has been employed as an electrolyte of a secondary battery such as a ZEBRA battery. Such molten salts of sodium aluminum chloride (NaAlCl ₄ ) have been found to be advantageous in terms of stability and ionic conductivity of sodium secondary batteries.

However, there was a limit in that the operating temperature of the secondary battery employing the sodium aluminum chloride (NaAlCl ₄ ) molten salt electrolyte reached substantially 300 ° C and was very high.

Therefore, according to the present invention, there is an attempt to provide a secondary battery capable of operating at a relatively low temperature by adopting an electrolyte for a sodium secondary battery having a low melting point and an excellent ion conductivity by improving such limitations.

The electrolyte of the sodium secondary battery according to an embodiment of the present invention may be a mixture of at least two kinds of salts. Specifically, the electrolyte of the sodium secondary battery may include at least one nitrile organic compound in the sodium molten salt. .

Here, the sodium molten salt of the electrolyte can be used without limitation as long as it is an electrolyte material that can be used as a molten salt electrolyte for a conventional sodium secondary battery. As a specific example of such a sodium molten salt, sodium aluminum chloride (NaAlCl ₄ ), sodium bromochloride (NaBrCl ₄ ), sodium iodide chloride (NaICl ₄ ) and the like are preferably used. In view of melting point, ionic conductivity and ionization degree, it may be most preferable to use aluminum chloride (NaAlCl _4).

The organic compound to be added to the sodium molten salt is preferably one or more selected from the group consisting of nitrile organic compounds in terms of excellent reducing resistance, excellent durability, lowered melting point and improved ionic conductivity can do. Specific and preferable examples of the nitrile organic compound according to an embodiment of the present invention may be one or more selected from adiponitrile, succinonitrile and sebaconitrile.

More specifically, it may be preferable to be succinonitrile in terms of lowering the melting point of the electrolyte, or may be adiponitrile, cevanonitrile or a mixture thereof in order to ensure efficient ion conductivity in battery operation while lowering the melting point. It may be more preferable to use a mixture.

The electrolyte according to an embodiment of the present invention may contain 99.9 to 80 wt% of sodium molten salt and 0.1 to 20 wt% of nitrile organic compound in order to efficiently lower the melting point of the electrolyte, It is preferable that 90 to 99 wt% of the sodium molten salt and 1 to 10 wt% of the nitrile organic compound are contained in order to ensure the ion conductivity for driving the battery while lowering the melting point of the electrolyte and reduce the manufacturing cost Lt; / RTI >

Specifically, if the content of the sodium molten salt in the electrolyte exceeds 99.9 wt% or the content of the nitrile organic compound is less than 0.1 wt%, the melting point of the electrolyte may not be lowered, and if the content of the sodium molten salt in the electrolyte is less than 80 wt% If the content of the organic compound is more than 20 wt%, the ion conductivity may be low and the battery may not be driven.

The electrolyte of the sodium secondary battery according to an embodiment of the present invention is composed of an electrolyte containing 99.9 to 80 wt% of sodium molten salt and 0.1 to 20 wt% of a nitrile organic compound as described above, surprisingly the electrolyte has a low melting point Specifically, the melting point of the electrolyte can be lowered to 150 ° C or less. Since the electrolyte is composed of an electrolyte in which the sodium molten salt and the nitrile organic compound are mixed, the nitrile organic compound may interfere with the stable crystalline state of the sodium molten salt and the lattice form may become unstable, thereby lowering the melting point of the electrolyte.

In addition, as described above, the ionic conductivity of the electrolyte is remarkably higher than a certain level even though the melting point of the electrolyte is lowered. Therefore, the secondary battery can be efficiently operated at a low temperature. Specifically, the ionic conductivity of the electrolyte is about Cm < 2 > at a temperature of 180 DEG C, preferably 200 ms / cm or more.

On the other hand, a sodium secondary battery employing the above-described electrolyte for a sodium secondary battery can be manufactured.

Specifically, as shown in FIG. 1, a sodium secondary battery according to an embodiment of the present invention includes a negative electrode containing sodium, a positive electrode containing a transition metal, and a sodium ion conductive solid electrolyte And the anode is impregnated with the electrolyte.

The electrolyte of the sodium secondary battery according to an embodiment of the present invention may be an electrolyte in which at least two kinds of salts are mixed. Specifically, the electrolyte of the sodium secondary battery may include a sodium molten salt and a nitrile organic compound. More specifically, the electrolyte of the sodium secondary battery may comprise 99.9 to 80 wt% of the sodium molten salt and 0.1 to 20 wt% of the nitrile organic compound.

Here, the sodium molten salt of the electrolyte can be used without limitation as long as it is an electrolyte material that can be used as a molten salt electrolyte for a conventional sodium secondary battery. As a specific example of such a sodium molten salt, sodium aluminum chloride (NaAlCl ₄ ), sodium bromochloride (NaBrCl ₄ ), sodium iodide chloride (NaICl ₄ ) and the like are preferably used. In view of melting point, ionic conductivity and ionization degree, it may be most preferable to use aluminum chloride (NaAlCl _4).

The organic compound to be added to the sodium molten salt is preferably one or more selected from the group consisting of nitrile organic compounds in terms of excellent reducing resistance, excellent durability, lowered melting point and improved ionic conductivity can do. Specific and preferable examples of the nitrile organic compound according to an embodiment of the present invention may be one or more selected from adiponitrile, succinonitrile and sebaconitrile.

More specifically, it may be preferable to be succinonitrile in terms of lowering the melting point of the electrolyte, or may be adiponitrile, cevanonitrile or a mixture thereof in order to ensure efficient ion conductivity in battery operation while lowering the melting point. It may be more preferable to use a mixture.

In addition, the structure of the electrolyte for a sodium secondary battery employed in the sodium secondary battery according to an embodiment of the present invention is as described above, and a detailed description thereof will be omitted since it is described above.

In the sodium secondary battery according to an embodiment of the present invention, the cathode may include a metal sodium or a sodium alloy. By way of non-limiting example, the sodium alloy may be sodium and cesium, sodium and rubidium or mixtures thereof. The negative electrode active material may be a solid phase or a liquid phase including a molten phase at an operating temperature of the battery. At this time, in order to realize a capacity of the battery of 50 Wh / kg or more, the negative electrode active material may be molten Na.

In the sodium secondary battery according to an embodiment of the present invention, the anode of the sodium secondary battery may contain a transition metal. The transition metal may include copper, silver, gold, nickel, palladium, platinum, cobalt, rhodium, iridium, iron, manganese, chromium, vanadium, molybdenum, ), Iron (Fe), manganese (Mn), cobalt (Co), and alloys thereof.

In the sodium secondary battery according to an embodiment of the present invention, the solid electrolyte is provided between the anode and the cathode, and may be composed of a sodium ion conductive solid electrolyte. At this time, the sodium ion conductive solid electrolyte physically separates the positive electrode and the negative electrode and may be a material having conductivity selectively to sodium ions, and a solid electrolyte conventionally used in the field of batteries for selective conduction of sodium ions suffices. As a non-limiting example, the solid electrolyte according to the present invention can be a sodium super ionic conductor (NaSICON), beta -alumina or beta "-alumina. Also, as a non-limiting example, (NASICON) is a complex oxide of Na-Zr-Si-O system, a complex oxide of Na-Zr-Si-PO system, a composite oxide of Y-doped Na-rZ- Si-PO-based composite oxide or a mixture thereof, and more specifically, Na ₃ Zr ₂ Si ₂ PO ₁₂ , Na _{1 + x} Si _x Zr ₂ P _{3 -x} O ₁₂ (1.6 <x <2.4 Y or Fe doped Na ₃ Zr ₂ Si ₂ PO ₁₂ , Y or Fe-doped Na _{1 + x} Si _x Zr ₂ P _3-x O ₁₂ (1.6 <x <2.4) .

In the sodium secondary battery according to an embodiment of the present invention, the sodium secondary battery is formed by separating the negative electrode and the positive electrode and separating the negative electrode space and the positive electrode space. The sodium secondary battery includes a flat plate Shaped battery structure or a tube-shaped battery structure including a tube-shaped solid electrolyte having one end closed.

Meanwhile, the sodium secondary battery according to an embodiment of the present invention can expect a charge / discharge reaction when a liquid electrolyte is employed in a battery operating temperature range. This charging / discharging reaction will be described in detail as a charge-discharge reaction according to the following Reaction Schemes 1 and 2.

In this case, in the following Reaction Schemes 1 and 2, when an electrolyte comprising succinonitrile and sodium aluminum chloride (NaAlCl ₄ ) is employed as the anode material, and the anode material is used as sodium chloride (NaCl) The present invention is not limited thereto. At this time, the electrolyte may contain 5 wt% (11.2 mol%) of succinonitrile.

The sodium secondary battery according to the present invention thus constructed is charged by the following Reaction Formula 1 and discharged according to the following Reaction Formula 2, and the charging and discharging reaction of such a battery can occur on the anode of the sodium secondary battery.

Scheme 1

_{Ni + 2NaCl -> NiCl 2 +} 2Na + + 2e -

Scheme 2

NiCl ₂ + 2Na ⁺ + 2e ^- - > Ni + 2NaCl

At this time, since the present invention is a sodium secondary battery, the alkali metal ion (i.e., sodium ion) generated by the charging reaction of the battery may be an ion conduction (transportation) material that is directly transferred to the cathode through the solid electrolyte in the battery. have. In addition, since the electrolyte according to the present invention is configured to include sodium ions, the sodium ion dissociated from the electrolyte can also act as an ion conduction (transporting) material, which is preferable in terms of improving ion conductivity of the sodium ion battery can do.

Meanwhile, a conventional sodium-based secondary battery must operate at a temperature of at least 250 ° C in the case of a sodium-nickel chloride battery and a minimum of 300 ° C or more in the case of a sodium-sulfur battery in consideration of the melting point of the conductivity and the battery constitution. There was a disadvantage of having an operating temperature.

However, since the electrolyte of the sodium secondary battery according to an embodiment of the present invention contains an organic compound together with the sodium molten salt, the organic compound interferes with the stable crystallization of the sodium molten salt in the electrolyte, resulting in deterioration of the ionic conductivity of the electrolyte It is possible to lower the melting point. Further, by employing such an electrolyte in a sodium secondary battery, it becomes possible to operate the battery at a relatively low temperature.

Specifically, the operation temperature of the sodium secondary battery according to an embodiment of the present invention may be 300 ° C or lower, more specifically, 120 ° C or higher and 300 ° C or lower. And more preferably 120 deg. C or higher and 200 deg. C or lower.

In addition, the ion conductivity of the electrolyte of the sodium secondary battery according to an embodiment of the present invention may be 100 ms / cm or more, preferably 200 ms / cm or more at a temperature of about 180 ° C.

Hereinafter, specific embodiments of the present invention will be described in detail.

[Electrolyte]

The organic compound according to the present invention was added to and mixed with NaAlCl ₄ sodium molten salt to prepare an electrolyte, and its melting temperature (melting point) and ionic conductivity were measured.

[Table 1]

At this time, the content of the organic compound (A) means the content of total organic compounds contained in the whole electrolyte, and was calculated according to the following formula.

Content of organic compound (wt%) = (A) weight / (A + B) weight x 100

Here, A is a nitrile organic compound, B is a sodium molten salt, (A) the weight is the total weight of the nitrile organic compound, and (A + B) weight means the total weight of the electrolyte.

Referring to Table 1, it can be seen that the melting points of the sodium secondary battery electrolytes Examples 1 to 3 according to the present invention are lower than those of the molten salt electrolytic solution comprising only sodium aluminum chloride (NaAlCl ₄ ) of Comparative Example 1. In addition, it can be confirmed that the ionic conductivities of Examples 1 to 3 also exhibit high efficiency exceeding a certain range. Although the ion conductivity of the electrolyte according to each of Examples 1 to 3 is not improved, the degree of ion conductivity can be selectively employed depending on the use of the battery. Specifically, the ion conductivity of the electrolyte according to the embodiment of the present invention is Cm &lt; 2 &gt; at a temperature of about 180 DEG C, preferably 200 ms / cm or more.

However, Embodiment 1 may be preferable from the viewpoint of lowering the melting point of the electrolyte, and Embodiment 2 or Embodiment 3 may be preferable from the viewpoint of ensuring efficient ion conductivity in battery driving while lowering the melting point.

[Operation of sodium secondary battery according to adoption of electrolyte]

It was confirmed that the sodium secondary battery was smoothly driven by cyclic voltametry potential waveform analysis of a sodium secondary battery manufactured in the form of a full cell according to the present invention. The cyclic voltammetry is an experiment to obtain the current value according to the current change. The experiment is performed so that the potential of the working electrode is returned from the initial potential to the original potential through oxidation (reduction), reduction potential (oxidation threshold potential) And a current value is obtained while converting the potential according to time.

Specifically, in this laboratory, a nickel (Ni) anode, a molten sodium cathode, and a NaSICON solid electrolyte were used. The anode was impregnated with the electrolytes of Comparative Examples 1 and 2 and 3 to prepare a sodium secondary battery Respectively.

Referring to FIG. 2, it can be seen that both cell type sodium secondary batteries (Example 2 and Example 3) produced according to the present invention operate smoothly at an operating temperature of about 180 ° C., It can be seen that the driving voltage range is improved as compared with the produced sodium secondary cell of Comparative Example 1 (Comparative Example 1).

INDUSTRIAL APPLICABILITY The sodium secondary battery according to the present invention employs an electrolyte having a lower melting point than that of a conventional sodium molten salt electrolyte and is capable of operating at a low temperature and preventing deterioration, thereby improving the lifetime of the battery and exhibiting high ionic conductivity, There is an advantage of having non-explosive properties.

In addition, the sodium secondary battery according to the present invention is advantageous in that it can be operated at a low temperature, thereby reducing manufacturing cost and securing stability.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Those skilled in the art will recognize that many modifications and variations are possible in light of the above teachings.

Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

1: Sodium secondary battery
10: cathode
30: anode
35: electrolyte
50: solid electrolyte

Claims (9)

99.9 to 80 wt% of a sodium molten salt and 0.1 to 20 wt% of a nitrile organic compound. The method according to claim 1,
Wherein the nitrile organic compound is at least one selected from adiponitrile, succinonitrile, and sebaconitrile. The method according to claim 1,
Wherein the sodium molten salt is sodium aluminum chloride. The method according to claim 1,
Wherein the electrolyte has a melting point of 150 DEG C or less. The method according to claim 1,
Wherein the electrolyte has an ion conductivity of 200 ms / cm or more when melted. A positive electrode impregnated with an electrolyte for a sodium secondary battery according to any one of claims 1 to 5 and comprising a transition metal;
An anode containing sodium; And
And a sodium ion conductive solid electrolyte provided between the cathode and the anode. The method according to claim 6,
Wherein the negative electrode comprises molten sodium. The method according to claim 6,
Wherein the anode comprises a metal selected from the group consisting of nickel, copper, iron, manganese, cobalt and alloys thereof. The method according to claim 6,
Wherein the sodium secondary battery has an operating temperature of 120 to 200 ° C.

Images