WO2015046852A1

WO2015046852A1 - Sodium secondary battery

Info

Publication number: WO2015046852A1
Application number: PCT/KR2014/008815
Authority: WO
Inventors: 채제현; 김정수; 박대인; 고원상; 이승옥; 박효승; 이광국; 김철우; 함진수
Original assignee: 에스케이이노베이션 주식회사
Priority date: 2013-09-25
Filing date: 2014-09-23
Publication date: 2015-04-02
Also published as: KR20150033866A; KR102203628B1

Abstract

The present invention relates to a sodium secondary battery which is capable of being operated at a low temperature by comprising a molten salt electrolyte having an adjusted melting point and, particularly, to a sodium secondary battery comprising: an anode which contains sodium; a cathode which contains transition metal and alkali metal halides; and a sodium ionic conducting solid electrolyte provided between the anode and the cathode, wherein the cathode is impregnated in a sodium molten salt electrolyte including an ether structure (-O-).

Description

Sodium secondary battery

The present invention relates to a sodium secondary battery, and more particularly, to a sodium secondary battery operable at a low temperature including a molten salt electrolyte having a melting point controlled.

As the use of renewable energy is increasing rapidly, the need for an energy storage device using a battery is increasing rapidly. Among these batteries, lead batteries, nickel / hydrogen cells, vanadium cells, and lithium batteries can be used. However, lead batteries and nickel / hydrogen batteries have a very small energy density, which requires a lot of space to store energy of the same capacity. In addition, in the case of vanadium battery, there is a problem that the performance is degraded due to the small amount of material between the negative electrode and the positive electrode through the membrane that separates the negative electrode and the positive electrode due to the environmental pollutant caused by using a solution containing heavy metals. It is not commercialized. In the case of a lithium battery having excellent energy density and output characteristics, it is technically very advantageous, but due to resource scarcity of the lithium material, there is a problem in that it is insufficient to be used as a secondary battery for large-scale power storage.

In order to solve this problem, many attempts have been made to use sodium, which is abundant on the earth, as a material for secondary batteries. Among them, as described in US Patent Publication No. 20030054255, a sodium sulfur battery in which beta alumina having selective conductivity for sodium ions is used, and sodium is supported on the negative electrode and sulfur on the positive electrode is currently used as a large-scale power storage device. .

However, conventional sodium-based secondary cells such as sodium-sulfur cells or sodium-nickel chloride cells should operate at least 250 ° C in the case of sodium-nickel chloride cells, taking into account the conductivity and melting points of the cell components. Sodium-sulfur cells have the disadvantage of having an operating temperature of at least 300 ° C or higher. Due to these problems, there are many disadvantages in terms of manufacturing or operation economics in order to reinforce the temperature maintenance, airtightness maintenance and safety aspects. In order to solve the above problems, room temperature-based sodium-based batteries have been developed, but the output is very low compared to nickel-hydrogen batteries or lithium batteries is very low.

An object of the present invention is to provide a sodium secondary battery that can be operated at a low temperature, and at the same time improved the output efficiency of the battery by employing a molten salt electrolyte that is melted at a low temperature as the melting point is adjusted as an electrolyte. In addition, the charging and discharging cycle characteristics are maintained for a long time to prevent deterioration, thereby providing a sodium secondary battery having an improved battery life and improved battery stability.

A negative electrode containing sodium according to the present invention; A positive electrode containing a transition metal and an alkali metal halide; And a sodium ion conductive solid electrolyte provided between the negative electrode and the positive electrode, and the positive electrode is impregnated into an electrolyte of Formula 1 below.

[Formula 1]

In formula 1, M is a metal or metalloid ion selected from the group of metals and metalloids having a trivalent oxidation number; R ₁ , R ₂ , R ₃ or R ₄ independently of one another are hydrogen, halogen, hydroxy, (C 1 -C 10) alkyl, trifluoromethanesulfonate or

Wherein at least one of R ₁ to R ₄ is trifluoromethanesulfonate or

R ₁₀ is (C 1 -C 10) alkyl, (C 1 -C 10) haloalkyl or (C 1 -C 10) alkylsilyl; Two R _{10 's} selected from R ₁ , R ₂ , R ₃ or R ₄ may be linked to each other with a (C 2 -C 10) alkylene or (C 2 -C 10) alkyleneoxy bond to form a ring; A is a single bond or -CO-; L ₁ and L ₂ are independently of each other a single bond or (C 1 -C 10) alkylene, and the alkylene of L ₁ and L ₂ may be further substituted with halogen or (C 1 -C 10) alkyl; a and b may be 0 or 1 independently of each other.

In the sodium secondary battery according to an embodiment of the present invention, M in Formula 1 may be boron ions, aluminum ions, gallium ions or indium ions.

In the sodium secondary battery according to an embodiment of the present invention, a + b ≧ 1 in Formula 1 may be satisfied.

In the sodium secondary battery according to an embodiment of the present invention, the electrolyte represented by Formula 1 may be represented by the following Formula 2 to Formula 4.

(Formula 2)

(Formula 3)

(Formula 4)

In formulas (2) to (4), M is a metal or metalloid ion selected from the group of metals and metalloids having a trivalent oxidation number; R ₁₁ , R _12, R ₁₃ and R ₁₄ are each independently hydrogen, (C 1 -C 10) alkyl, (C 1 -C 10) alkoxy, (C 1 -C 10) haloalkyl, (C 1 -C 10) alkoxyalkyl, (C 1- C10) haloalkoxyalkyl, (C1-C10) alkoxyalkoxyalkyl, (C1-C10) alkylsilyl, trifluoromethanesulfonyl or

Alkyl, alkoxy, haloalkyl, alkoxyalkyl, haloalkoxyalkyl, alkoxyalkoxyalkyl and alkylsilyl may be further substituted with halogen or (C1-C10) alkyl; A is a single bond or -CO-; Z is

Or -CO-; x is an integer of 0 to 4, y is an integer of 1 to 4, a, b and c may be an integer of 1 to 5.

In the sodium secondary battery according to an embodiment of the present invention, Formula 1 may be selected from the following compounds.

In the sodium secondary battery according to an embodiment of the present invention, the negative electrode may include metal sodium or a sodium compound.

In the sodium secondary battery according to an embodiment of the present invention, the molten salt electrolyte may have a melting point of 200 ° C or less.

In the sodium secondary battery according to an embodiment of the present invention, the molten salt electrolyte may have a viscosity of 0.1 to 10000 cps.

In the sodium secondary battery according to an embodiment of the present invention, the molten salt electrolyte may further include a dissociation inducing agent.

In the sodium secondary battery according to an embodiment of the present invention, the dissociation inducing agent may be a crown ether, Lewis acid or a mixture thereof.

In the sodium secondary battery according to an embodiment of the present invention, the crown ether may be one or a mixture of two or more selected from the following structural formulas.

In a sodium secondary battery according to an embodiment of the present invention, the Lewis acid is aluminum chloride (AlCl ₃ ), aluminum iodide (AlI ₃ ), zinc chloride (ZnCl ₂ ), zinc iodide (ZnI ₂ ), or boron chloride (BCl ₃ ) One or more of boron fluoride (BF ₃ ) and tris (pentafluorophenyl) borane (TPFPB).

In the sodium secondary battery according to an embodiment of the present invention, the molar ratio of the crown ether: Lewis acid of the mixture may be 1: 0.1 to 10.

In the sodium secondary battery according to an embodiment of the present invention, the molten salt electrolyte may include a dissociation inducing agent of 10 M to 1000 mM molar concentration.

In the sodium secondary battery according to the present invention, by employing an electrolyte containing an ether structure (-O-), the melting point of the electrolyte is controlled to enable operation of the battery at a low temperature, and the output efficiency of the battery is significantly improved. It is effective.

In addition, according to the present invention, a sodium secondary battery employing a molten salt electrolyte having a controlled melting point has a stable charge / discharge cycle characteristics for a long time, thereby preventing deterioration, thereby improving battery life and improving battery stability. .

1 is a conceptual diagram schematically showing the structure of a sodium secondary battery 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 drawings introduced below are provided by way of example so that the spirit of the invention to those skilled in the art can fully convey. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. Also, like reference numerals denote like elements throughout the specification.

At this time, if there is no other definition in the technical terms and scientific terms used, it has a meaning commonly understood by those of ordinary skill in the art to which the present invention belongs, the gist of the present invention in the following description and the accompanying drawings Descriptions of well-known functions and configurations that may be unnecessarily blurred are omitted.

The electrolyte of the sodium secondary battery according to the present invention may be a molten salt electrolyte, specifically, the molten salt electrolyte of the sodium secondary battery according to an embodiment of the present invention is represented by the following [Formula 1].

[Formula 1]

(In Formula 1, M is a metal or metalloid ion selected from the group of metals and metalloids having a trivalent oxidation number; R ₁ , R ₂ , R ₃ or R ₄ are independently of each other hydrogen, halogen, hydroxy, ( C1-C10) alkyl, trifluoromethanesulfonate or Wherein at least one of R ₁ to R ₄ is trifluoromethanesulfonate or

R ₁₀ is (C 1 -C 10) alkyl, (C 1 -C 10) haloalkyl or (C 1 -C 10) alkylsilyl; Two R _{10 's} selected from R ₁ , R ₂ , R ₃ or R ₄ may be linked to each other with a (C 2 -C 10) alkylene or (C 2 -C 10) alkyleneoxy bond to form a ring; A is a single bond or -CO-; L ₁ and L ₂ are independently of each other a single bond or (C 1 -C 10) alkylene, and the alkylene of L ₁ and L ₂ may be further substituted with halogen or (C 1 -C 10) alkyl; a and b may be 0 or 1 independently of each other.)

At this time, the molten salt electrolyte constituting the sodium secondary battery according to the present invention represented by [Formula 1] includes an ether (Ether) structure (-O-), the molecular group around the oxygen (O) atoms of the ether structure It is easy to rotate (rotation) of the melting point and the viscosity of the molten salt electrolyte can be adjusted low. Here, the ether structure means a bond of a 'metal atom-oxygen atom-hydrocarbon molecule' as represented in [Formula 1], and the atom or the center of the oxygen atom in the 'hydrocarbon molecule' according to the embodiment of the present invention. The molecule may further comprise at least one further ether structure bonded to both sides.

Specifically, the molten salt electrolyte of the sodium secondary battery according to the present invention may be composed of sodium ions and monovalent anion molecular groups, more specifically, the molecular weight or molecular structure form of the molten salt electrolyte according to an embodiment of the present invention Can be determined primarily by the size of the anionic molecular group bound to the sodium ions.

Here, the anion molecular group may be formed by combining metal ions (M; hereinafter, including metalloid ions) and four functional groups, as shown in [Formula 1]. At this time, M is one metal ion selected from the group of metals having a trivalent oxidation number, specifically M is preferably a metal or metalloid ion selected from the Group 13 metal group, more preferably aluminum ions, boron ions and gallium Selecting a selected one of the ions may be advantageous to construct the molten salt electrolyte. That is, the molten salt electrolyte according to the present invention is composed of a molten salt selected from sodium-aluminum salt, sodium-boron salt, and sodium-gallium salt according to the selected metal ion, to prevent the explosion of the secondary battery electrolyte and stable melting The state can be guaranteed.

Four functional groups bonded to the metal ion (M) thus constructed are R ₁ , R ₂ , R ₃ or R ₄ , and each functional group is independently of each other hydrogen, halogen, hydroxy, (C 1 -C 10) alkyl. , Trifluoromethanesulfonate or

Can be selected from. That is, the oxygen atom and the four functional groups selected above are bonded to the metal ion, and the oxygen atom is disposed between the metal ion and the functional group, and the structure is easily rotated due to the ether structure connected to the oxygen atom. Can be generated to lower the melting point of the molten salt electrolyte.

At this time, in the sodium secondary battery according to an embodiment of the present invention, the molten salt electrolyte employed in the sodium secondary battery

When represented by, the hydrocarbon molecule may include a straight chain structure and a branched chain structure and the like according to a predetermined condition. At this time, A, L ₁ , L ₂ , a and b for setting the structure of the hydrocarbon molecule determine the chain length of the functional group may be a major factor affecting the size of the molten salt electrolyte. And, according to the setting of A, L ₁ , L ₂ , a and b may be configured to further include an ether structure in a hydrocarbon molecule. And, R ₁₀ may be a haloalkyl silyl or (C1 ~ C10) alkyl (C1 ~ C10) alkyl, (C1 ~ C10).

Specifically

A may be a single bond or -CO-. When A is -CO-, a protruding portion is formed in the functional group to have an asymmetric structure in the functional group, thereby acting as a factor that further induces rotation of the functional group structure.

Also,

L ₁ and L ₂ may be selected independently from each other of a single bond or (C1 ~ C10) alkylene. Wherein L ₁ and L ₂ will determine the overall length of the functional group and thereby can act as a factor directly affecting the molecular weight and molecular size of the functional group. Wherein L ₁ and L ₂ are independently selected and may be the same or different. In this case, it may be preferable that L ₁ and L ₂ do not exceed the size of (C10) alkylene. This is because when L ₁ and L ₂ exceed the size of (C10) alkylene, the chain length of the functional group becomes longer and the molecular weight is excessively increased, which makes it difficult to induce rotation in the functional group. In addition, as the rotation of the functional group is inhibited, it may also be difficult to control the melting point and viscosity of the molten salt electrolyte low.

Also,

A and b may be selected independently from each other at 0 or 1. Where a and b are

It determines the number of ether structures included in the functional group determined by it can act as a factor affecting the degree of rotation of the functional group. In this case, the number of ether structures included in the functional group is not particularly limited, but in the aspect of lowering excessive melting energy by limiting the overall molecular size in the sodium secondary battery of the present invention, the ether structure (-O-) included in one functional group is It may be desirable not to exceed a maximum of three. Here, the maximum of three may mean that the ether structure included in the 'metal atom-oxygen atom-hydrocarbon molecule' and the ether structure when both a and b are 1. It may also be desirable for a and b to satisfy the range a + b ≧ 1. That is, it may be preferable that at least one of a and b is 1. Because, when the molecular weight of the molten salt electrolyte is relatively large, the ether structure included in the 'metal atom-oxygen atom-hydrocarbon molecule' in the functional group alone may be difficult to induce easy rotation. Because it can be induced.

Also,

R ₁₀ may be (C 1 -C 10) alkyl, (C 1 -C 10) haloalkyl or (C 1 -C 10) alkylsilyl. The size of the R ₁₀ is a non-limiting and, by limiting the overall molecular size in the sodium secondary battery of the present invention carbon atoms contained in R ₁₀ in terms of lowering the melting energy may preferably be up to 10.

As described above, _four functional groups R ₁ , R ₂ , R _3, or R ₄ are independently configured to be bonded to one metal ion (M), thereby forming an anionic molecular group. In this case, each functional group may be formed in the same or different structure. Preferably, when four functional groups constituting the anion molecular group are selected and formed in the same structure, the structure of the anion molecular group is in a regular state than when formed in a different structure, so that rotation by the ether structure contained in the anion molecular group is further improved. It may be advantageous to further lower the melting point and viscosity of the molten salt electrolyte employed in the sodium secondary battery according to the present invention, it may be advantageous to predict the degree of reduction of the melting point due to the selected employed structure.

Meanwhile, two R _{10 's} selected from four functional groups R ₁ , R ₂ , R _3, or R ₄ connected to the metal ion M may be connected to each other to form a ring. Specifically, the ends of two R ₁₀ selected from R ₁ , R ₂ , R ₃ or R ₄ may form a ring with a (C 2 -C 10) alkylene or (C 2 -C 10) alkyleneoxy bond.

In detail, the molten salt electrolyte of the sodium secondary battery of the present invention configured as described above may be one or a mixture of two or more selected from the group consisting of the following Chemical Formulas 2 to 4.

(Formula 2)

(Formula 3)

(Formula 4)

In formulas (2) to (4), M is the same as the metal ion (M) described above as a metal or metalloid ion selected from the group of metals and metalloids having a trivalent oxidation number; R ₁₁ , R _12, R ₁₃ and R ₁₄ are each independently hydrogen, (C 1 -C 10) alkyl, (C 1 -C 10) alkoxy, (C 1 -C 10) haloalkyl, (C 1 -C 10) alkoxyalkyl, (C 1- C10) haloalkoxyalkyl, (C1-C10) alkoxyalkoxyalkyl, (C1-C10) alkylsilyl, trifluoromethanesulfonyl or

Or -O-; x is an integer of 0 to 4, y is an integer of 1 to 4, a, b and c may be an integer of 1 to 5. here

The functional group represented by may be configured as described above.

Embodiments of the molten salt electrolyte configured according to the above may be selected from the chemical formulas and structural formulas shown in the following [Table 1], but it will be obvious that it can be extended within the range satisfying the present invention.

Table 1

division	Chemical formula	constitutional formula
Example 1	NaAl (OCH ₂ CH ₂ OCH ₃ ) ₄
Example 2	NaAl (OCHCH ₃ OCH ₃ ) ₄
Example 3	NaAl (OCH ₃ ) ₄
Example 4	NaAl (OCH ₂ CF ₃ ) ₄
Example 5	NaAl (OC (CH ₃ ) ₃ ) ₄
Example 6	NaB (OCH ₂ CH ₂ OCH ₃ ) ₄
Example 7	NaAl (OCH ₂ CH ₂ OCH ₂ CH ₃ ) ₄
Example 8	_{_{_{NaAl (OCH 2 CH 2 OCH 2}}} CH 2 OCH 3) 4
Example 9	NaB (OCH ₂ CH ₂ OCH ₂ CH ₃ ) ₄
Example 10	NaAl (OCH ₂ CH ₂ OCH ₂ CH ₂ OCH ₂ CH ₂ O) ₂
Example 11	NaAl (OCH ₂ CH ₂ OCH ₂ CH ₂ O) ₂
Example 12	NaAl (OCH ₂ CH ₂ OCH ₂ CF ₃ ) ₄
Example 13	NaB (OCH ₂ CH ₂ OCH ₂ CH ₂ OCH ₃ ) ₄
Example 14	NaAl (COOCH ₂ OCH ₂ CH ₂ OCH ₃ ) ₄
Example 15	NaAl (COOCH ₂ OCH ₂ CH ₂ OCH ₃ ) ₂ (OCH ₂ CH ₂ OCH ₃ ) ₂
Example 16	NaAl (OSi (CH ₃ ) ₃ ) ₂ (OCH ₂ CH ₂ OH ₃ ) ₂
Example 17	NaB (COOCH ₃ ) ₃ (OCH ₂ CF ₃ )
Example 18	_{_{NaAl (COOCF 3) 2 (OCH}} 2 CH 2 OCH 3) 2
Example 19	NaAl (SO ₃ CF ₃ ) ₂ (OCH ₂ CH ₂ OCH ₃ ) ₂
Example 20	NaAl (SO ₃ CF ₃ ) ₄
Example 21	NaAlCl ₃ (OCH ₂ CH ₂ OCH ₂ CH ₂ OCH ₃ )

Experimental Example

Melting point measurement of molten salt electrolyte

Melting points of the embodiments of the molten salt electrolyte according to the present invention are shown in Table 2 below.

TABLE 2

division	Chemical formula	Melting Point (Mp; ℃)
Example 1	NaAl (OCH ₂ CH ₂ OCH ₃ ) ₄	135
Example 7	NaAl (OCH ₂ CH ₂ OCH ₂ CH ₃ ) ₄	70
Example 8	NaAl (OCH ₂ CH ₂ OCH ₂ CH ₂ OCH ₃ ) ₄	Liquid
Example 12	NaAl (OCH ₂ CH ₂ OCH ₂ CF ₃ ) ₄	85
Example 13	NaB (OCH ₂ CH ₂ OCH ₂ CH ₂ OCH ₃ ) ₄	Liquid
Example 14	NaAl (COOCH ₂ OCH ₂ CH ₂ OCH ₃ ) ₄	160
Example 15	NaAl (COOCH ₂ OCH ₂ CH ₂ OCH ₃ ) ₂ (OCH ₂ CH ₂ OCH ₃ ) ₂	100
Example 16	NaAl (OSi (CH ₃ ) ₃ ) ₂ (OCH ₂ CH ₂ OH ₃ ) ₂	110
Example 18	NaAl (COOCF ₃ ) ₂ (OCH ₂ CH ₂ OCH ₃ ) ₂	130
Example 19	NaAl (SO ₃ CF ₃ ) ₂ (OCH ₂ CH ₂ OCH ₃ ) ₂	120

Here, the liquid state means that the molten salt electrolyte is in a liquid state at room temperature.

Referring to Table 2, the molten salt electrolyte according to the present invention exhibits a low melting point of 200 ° C. or less, thereby confirming the effect of enabling sodium battery operation at low temperatures.

In addition, the molten salt electrolyte configured as described above may vary depending on conditions such as concentration and purity, but may have a viscosity of 0.1 to 10000 cps. In this case, when the viscosity of the molten salt electrolyte exceeds 10000cps, the melting point may be increased due to excessive viscosity.

On the other hand, the sodium secondary battery according to the present invention employing the molten salt electrolyte is configured as described above, it is possible to maintain a stable molten state at the operating temperature and pressure of the secondary battery, it is easy to diffuse the sodium ions introduced through the solid electrolyte It can be very excellent in terms of stability of charge and discharge cycle characteristics and improvement of storage characteristics which can prevent self discharge without causing unwanted side reactions.

Specifically, such a sodium secondary battery may be composed of a positive electrode impregnated in a negative electrode, a solid electrolyte and a molten salt electrolyte.

In the sodium secondary battery according to an embodiment of the present invention, the negative electrode of the sodium secondary battery may include a metal sodium or sodium alloy. Specifically, the negative electrode of the sodium secondary battery may be a halide of sodium halide or sodium alloy material.

In the sodium secondary battery according to an embodiment of the present invention, the positive electrode of the sodium secondary battery may contain a transition metal and an alkali metal halide. At this time, the transition metal may include copper, silver, gold, nickel, palladium, platinum, cobalt, rhodium, iridium, iron, manganese, chromium, vanadium, molybdenum, and the like, preferably nickel (Ni), copper (Cu ) And iron (Fe). In addition, as the alkali metal halide, sodium halide (NaX; X = halide) may be employed, in which case fluoride (F), chlorine (Cl), bromine (Br), iodine (I), Astaxin (At) may be all but it may be preferable to employ chlorine (Cl), bromine (Br) and iodine (I).

In the sodium secondary battery according to an embodiment of the present invention, the positive electrode of the sodium secondary battery may be impregnated in the molten salt electrolyte represented by the above [Formula 1].

The sodium secondary battery according to the present invention configured as described above may be charged by the following Scheme 1 and discharge may be made by the following Scheme 2.

Scheme 1

mNaX + M ¹ → mNa + M ¹ Xm

Scheme 2

mNa + M ¹ Xm → mNaX + M ¹

In Scheme 1 and Scheme 2, M ¹ is a metal selected from one or more of the transition metal group, X is a halogen element, m is a natural number of 1 to 4. Specifically, m in Scheme 1 and Scheme 2 may be a natural number corresponding to the valence of the amount of the metal (M ¹ ).

In addition, in the detailed description of the sodium secondary battery according to an embodiment of the present invention, for a clearer understanding, reaction products or materials (sodium halides, transition metal halides, etc.) during the charge and discharge reactions of Schemes 1 and 2 On the basis of the above, the positive electrode and the charge / discharge reaction were described in detail.

And, in the sodium secondary battery according to an embodiment of the present invention, the solid electrolyte is provided between the positive electrode and the negative electrode, it may be composed of a sodium ion conductive solid electrolyte. At this time, the sodium ion conductive solid electrolyte may be a material that physically separates the positive electrode and the negative electrode and has a selective conductivity with respect to sodium ions, and may be a solid electrolyte commonly used in the battery field for selective conduction of sodium ions. As a non-limiting example, the solid electrolyte of the present invention may be a sodium super ionic conductor (NaSICON), β-alumina or β ″ -alumina. Also, as a non-limiting example, sodium superion conductor ( NASICON) is Na-Zr-Si-O based composite oxide, Na-Zr-Si-PO based composite oxide, Y doped Na-Zr-Si-PO based composite oxide, Fe doped Na-Zr-Si -PO-based composite oxides or mixtures thereof may be included, and in detail, 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 real) ), 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 (real number 1.6 <x <2.4) or mixtures thereof can do.

In the sodium secondary battery according to an embodiment of the present invention, based on the shape of the solid electrolyte which separates the negative electrode and the positive electrode to partition the negative electrode space and the positive electrode space, the sodium secondary battery is a flat plate comprising a solid electrolyte of the flat plate shape It may have a tubular battery structure or a tubular battery structure comprising a tubular solid electrolyte of one end sealed.

On the other hand, in the sodium secondary battery according to an embodiment of the present invention, the molten salt electrolyte of the sodium secondary battery may further include a dissociation inducing agent. Wherein the dissociation inducing agent may be selected from crown ethers, Lewis acids or mixtures thereof.

Specifically, as the dissociation inducing agent according to an embodiment of the present invention, the crown ether is a crown-shaped complex made of polyether, and an oxyethylene group is formed in the form of-(OCH ₂ CH ₂ ) n- to form a large ring-shaped polyethylene ether skeleton. It means a compound having a.

Specifically, it may be one or a mixture of two or more selected from the structural formulas shown below.

In such crown ethers, the ionization degree of the molten salt electrolyte can be improved by directly dissociating the molten salt electrolyte by coordinating the oxygen element (O) of the crown ether with sodium ions (Na ⁺ ) of the molten salt electrolyte. For example, the sodium-aluminum salt of Example 1, in which the metal ion (M) of the above-described formula (M) is aluminum (Al), is used as a molten salt electrolyte, and glucose, which is a crown ether as a dissociation inducing agent ( When C ₁₂ H ₂₄ O ₆ ) is added, sodium ions (Na ⁺ ) are coordinated to the coordination site of glucose (C ₁₂ H ₂₄ O ₆ ), and sodium-aluminate salt (Na Aluminate) according to the reaction of Scheme 3 below. salt) can be dissociated to improve the degree of ionization of the molten salt electrolyte.

Scheme 3

In addition, in addition to the dissociation induction agent, a separate sodium salt may be further added to the molten salt electrolyte employed in the sodium secondary battery according to the present invention. In this case, the dissociation induction agent coordinates the sodium ions of the added sodium salt to the molten salt electrolyte. Can further improve the degree of ionization.

In addition, the Lewis acid included as the dissociation inducing agent is an electron pair acceptor according to the Lewis definition, specifically, a compound containing an unshared electron pair, aluminum chloride (AlCl ₃ ), aluminum iodide (AlI ₃ ), zinc chloride (ZnCl ₂ ), and iodide Zinc (ZnI ₂ ), boron chloride (BCl ₃ ), boron fluoride (BF ₃ ) and tris (pentafluorophenyl) borane (TPFPB; Tris (pentafluorophenyl) borane). The dissociation inducing agent composed of Lewis acid can improve the ionization degree of the molten salt electrolyte by increasing the amount of free-sodium ion (free-Na ⁺ ) in the molten salt electrolyte by attracting anions of the molten salt electrolyte to dissociate the molten salt electrolyte. have. For example, Example 8 sodium aluminum salt (Na Aluminate salt) in which the metal ion (M) of the above-described formula (M) is aluminum (Al) as a molten salt electrolyte is included and tris (pentafluorophenyl) as a dissociation inducing agent. When borane (TPFPB) is added, sodium ions (Na ⁺ ) become free in the molten salt electrolyte according to the reaction of Scheme 4 below to improve the ionization degree of the molten salt electrolyte.

Scheme 4

In addition, in addition to the dissociation induction agent, a separate sodium salt may be further added to the molten salt electrolyte employed in the sodium secondary battery according to the present invention. In this case, the dissociation induction agent attracts anions of the added sodium salt to ionize the molten salt electrolyte. Can be further improved.

Alternatively, the electrolyte of the sodium secondary battery according to an embodiment of the present invention may include a mixture of the crown ether and Lewis acid as a dissociation inducing agent. That is, as described above, the crown ether coordinates the cation to dissociate the alkali metal halide of the positive electrode, and Lewis acid dissociates the alkali metal halide of the positive electrode by attracting anions. Therefore, when such a mixture of crown ether and Lewis acid is contained as a dissociation inducing agent, the ionization degree of the molten salt electrolyte can be significantly improved by inducing dissociation of the cation and the anion of the alkali metal halide simultaneously.

At this time, the dissociation inducing agent contained in the molten salt electrolyte employed in the sodium secondary battery according to the present invention may contain a dissociation inducing agent of 10 μM to 1000 mM molar concentration. Herein, when the content of the dissociation inducing agent in the molten salt electrolyte is less than 10 μM, the effect of improving the conductivity of the ions in the molten salt electrolyte by the dissociating inducing agent may be insignificant, and the conductivity of the ions participating in the electrochemical reaction of the battery, such as sodium ions. The efficiency of the battery may decrease, and the capacity of the battery itself may be too low. In addition, when the content of the dissociation inducing agent in the molten salt electrolyte is more than 1000mM molar concentration, the ion concentration in the molten salt electrolyte is excessively increased, which may cause a risk of overheating during discharge of the battery, and the number of ions combined with the dissociation inducing agent is relatively high. Too many can lead to a decrease in ionic conductivity as a whole due to the lack of free-ion in the electrolyte. Therefore, when the content of the dissociation inducing agent in the molten salt electrolyte is 10μM to 1000mM molar concentration, it is possible to obtain an optimal result that the overheating of the battery does not occur while the conductivity of the ions in the molten salt electrolyte is improved.

When the molten salt electrolyte employed in the sodium secondary battery according to the present invention contains a mixture of crown ether and Lewis acid as a dissociation inducing agent, the mixture may be mixed with a molar ratio of crown ether: Lewis acid of 1: 0.1 to 10. have. The molar ratio of the crown ether: Lewis acid affects the degree of dissociation of the molten salt electrolyte. If the molar ratio of Lewis acid to less than 0.1 mol of the molten salt electrolyte is less than 0.1 mol, pre-sodium ions due to dissociation of the molten salt electrolyte (free- The increase of Na ⁺ ) is relatively small, and if the molar ratio of Lewis acid to 1 mole of crown ether is more than 10 moles, the increase in free-anion due to dissociation of the molten salt electrolyte is relatively insignificant. can do.

On the other hand, conventional sodium-based secondary cells should operate at least 250 ° C in the case of sodium-nickel chloride cells, and at least 300 ° C in the case of sodium-sulfur cells, in consideration of the melting point of the conductivity and cell composition. There was a disadvantage of having an operating temperature.

However, the sodium secondary battery according to the present invention can not only increase the ionic conductivity of the sodium secondary battery by adopting a molten salt electrolyte having a melting point and viscosity controlled due to the limitation of carbon number and structural characteristics, but also at a relatively low temperature. It may be possible to implement a capacity of 50 Wh / kg or more. Specifically, the operating temperature of the sodium secondary battery according to the present invention may be 200 ° C or less, more specifically 120 ° C to 200 ° C or less.

1 is a sodium secondary battery, 10 is a negative electrode, 30 is a positive electrode, 35 is a positive electrolyte and 50 is a solid electrolyte.

Claims

Negative electrode containing sodium;

A positive electrode containing a transition metal and an alkali metal halide; And

It comprises a sodium ion conductive solid electrolyte provided between the cathode and the anode,

Sodium secondary battery is the positive electrode impregnated in the electrolyte of the formula (1).

[Formula 1]

(In Formula 1, M is a metal or metalloid ion selected from the group of metals and metalloids having a trivalent oxidation number;

R 1 , R 2 , R 3 or R 4 are independently of each other hydrogen, halogen, hydroxy, (C 1 -C 10) alkyl, trifluoromethanesulfonate or
Wherein at least one of R 1 to R 4 is trifluoromethanesulfonate or
Take it,

R 10 is (C 1 -C 10) alkyl, (C 1 -C 10) haloalkyl or (C 1 -C 10) alkylsilyl;

Two R 10 's selected from R 1 , R 2 , R 3, or R 4 may be linked to each other by a (C 2 -C 10) alkylene or (C 2 -C 10) alkyleneoxy bond to form a ring;

A is a single bond or -CO-;

L 1 and L 2 are each independently a single bond or (C1-C10) alkylene,

The alkylene of L 1 and L 2 may be further substituted with halogen or (C 1 -C 10) alkyl;

A and b are each independently 0 or 1.)
The method of claim 1,

In Formula 1, M is a boron ion, aluminum ion, gallium ion or indium ion sodium secondary battery.
The method of claim 1,

Sodium secondary battery that satisfies a + b ≥ 1 in the formula (1).
The method of claim 1,

The electrolyte represented by Formula 1 is a sodium secondary battery represented by the following Formula 2 to Formula 4.

(Formula 2)

(Formula 3)

(Formula 4)

(In Formula 2 to Formula 4,

M is a metal or metalloid ion selected from the group of metals and metalloids having a trivalent oxidation number;

R 11 , R 12, R 13 and R 14 are each independently hydrogen, (C 1 -C 10) alkyl, (C 1 -C 10) alkoxy, (C 1 -C 10) haloalkyl, (C 1 -C 10) alkoxyalkyl, (C 1 -C10) haloalkoxyalkyl, (C1-C10) alkoxyalkoxyalkyl, (C1-C10) alkylsilyl, trifluoromethanesulfonyl or
ego,

The alkyl, alkoxy, haloalkyl, alkoxyalkyl, haloalkoxyalkyl, alkoxyalkoxyalkyl and alkylsilyl may be further substituted with halogen or (C1-C10) alkyl;

A is a single bond or -CO-;

Z is
Or -O-;

X is an integer of 0 to 4,

Y is an integer of 1 to 4,

A, b and c are integers from 1 to 5.)
The method of claim 1,

Formula 1 is a sodium secondary battery selected from the following compounds.
The method of claim 1,

The negative electrode is a sodium secondary battery containing a metal sodium or sodium compound.
The method of claim 1,

The molten salt electrolyte has a sodium secondary battery having a melting point of 200 ℃ or less.
The method of claim 1,

The molten salt electrolyte is a sodium secondary battery having a viscosity of 0.1 to 10000 cps.
The method of claim 1,

The molten salt electrolyte further comprises a sodium secondary battery dissociation inducing agent.
The method of claim 9,

The dissociation inducing agent is a sodium secondary battery is a crown ether, Lewis acid or a mixture thereof.
The method of claim 10,

The crown ether is a sodium secondary battery is one or a mixture of two or more selected from the following structural formula.
The method of claim 10,

The Lewis acids include aluminum chloride (AlCl 3 ), aluminum iodide (AlI 3 ), zinc chloride (ZnCl 2 ), zinc iodide (ZnI 2 ), boron chloride (BCl 3 ), boron fluoride (BF 3 ) and tris (pentafluoro) Sodium secondary battery selected from one or more of phenyl) borane (TPFPB).
The method of claim 10,

Sodium secondary battery of the mixture of crown ether: Lewis acid molar ratio of 1: 0.1 to 10.
The method of claim 9,

The molten salt electrolyte is a sodium secondary battery comprising the dissociation inducing agent of 10μM to 1000mM molar concentration.